diff --git a/README.md b/README.md
index 0c7366c..564be62 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,7 @@ The exercises related to OpenMP programming model can be found in the folder `op
 - `cuda\lab1`: CUDA Basics
 - `cuda\lab2`: CUDA Memory Model
 - `cuda\lab3`: CUDA Advanced Host Management
+- `cuda\appendix`: CUDA Nsight Tutorial
 
 ### (Optional)
 - `challenge`: Parallelize the code with everything you learned and submit the result before *21 May 2021*
diff --git a/cuda/appendix/.gitignore b/cuda/appendix/.gitignore
new file mode 100644
index 0000000..47b77e5
--- /dev/null
+++ b/cuda/appendix/.gitignore
@@ -0,0 +1,6 @@
+Release/
+Debug/
+
+.ptp-sync
+.settings
+.ptp-sync-folder
diff --git a/cuda/appendix/OpenCV-Config.txt b/cuda/appendix/OpenCV-Config.txt
new file mode 100644
index 0000000..bdcc182
--- /dev/null
+++ b/cuda/appendix/OpenCV-Config.txt
@@ -0,0 +1,21 @@
+# Add Include Dir
+/usr/include/opencv4/opencv
+/usr/include/opencv4
+
+# Add Libs
+opencv_dnn
+gomp
+opencv_gapi
+opencv_highgui
+opencv_ml
+opencv_objdetect
+opencv_photo
+opencv_stitching
+opencv_video
+opencv_calib3d
+opencv_features2d
+opencv_flann
+opencv_videoio
+opencv_imgcodecs
+opencv_imgproc
+opencv_core
\ No newline at end of file
diff --git a/cuda/appendix/gemm/gemm.cu b/cuda/appendix/gemm/gemm.cu
new file mode 100644
index 0000000..fc73a49
--- /dev/null
+++ b/cuda/appendix/gemm/gemm.cu
@@ -0,0 +1,246 @@
+/*
+ * BSD 2-Clause License
+ * 
+ * Copyright (c) 2020, Alessandro Capotondi
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ * 
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @file gemm.cu
+ * @author Alessandro Capotondi
+ * @date 12 May 2020
+ * @brief GEMM Kernel
+ * 
+ * @see https://dolly.fim.unimore.it/2019/course/view.php?id=152
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#define gpuErrchk(ans)                        \
+    {                                         \
+        gpuAssert((ans), __FILE__, __LINE__); \
+    }
+static inline void gpuAssert(cudaError_t code, const char *file, int line, bool abort = true)
+{
+    if (code != cudaSuccess)
+    {
+        fprintf(stderr, "GPUassert: %s %s %d\n", cudaGetErrorString(code), file, line);
+        if (abort)
+            exit(code);
+    }
+}
+
+#define TWO02 (1 << 2)
+#define TWO04 (1 << 4)
+#define TWO08 (1 << 8)
+
+#ifndef N
+#define N (1 << 10)
+#endif
+#ifndef TILE_W
+#define TILE_W 128
+#endif
+#ifndef BLOCK_SIZE
+#define BLOCK_SIZE 32
+#endif
+
+#define SM 64
+static void reorder(float *__restrict__ a, float *__restrict__ b, int n)
+{
+    for (int i = 0; i < SM; i++)
+        for (int j = 0; j < SM; j++)
+            b[i * SM + j] = a[i * n + j];
+}
+
+static void mm(float *__restrict__ a, float *__restrict__ b, float *__restrict__ c, int n)
+{
+    for (int i = 0; i < SM; i++)
+    {
+        for (int k = 0; k < SM; k++)
+        {
+            for (int j = 0; j < SM; j++)
+            {
+                c[i * n + j] += a[i * n + k] * b[k * SM + j];
+            }
+        }
+    }
+}
+void gemm_host(float *a, float *b, float *c, int n)
+{
+    int bk = n / SM;
+#pragma omp parallel for collapse(3)
+    for (int i = 0; i < bk; i++)
+    {
+        for (int j = 0; j < bk; j++)
+        {
+            for (int k = 0; k < bk; k++)
+            {
+                float b2[SM * SM];
+                reorder(&b[SM * (k * n + j)], b2, n);
+                mm(&a[SM * (i * n + k)], b2, &c[SM * (i * n + j)], n);
+            }
+        }
+    }
+}
+__global__ void gemm(float *__restrict__ a, float *__restrict__ b, float *__restrict__ c, int n)
+{
+    __shared__ float As[BLOCK_SIZE][BLOCK_SIZE];
+    __shared__ float Bs[BLOCK_SIZE][BLOCK_SIZE];
+
+    int ib = blockIdx.y;
+    int jb = blockIdx.x;
+
+    int it = threadIdx.y;
+    int jt = threadIdx.x;
+
+    int a_offset, b_offset, c_offset;
+
+    float Cvalue = 0.0f;
+    for (int kb = 0; kb < (n / BLOCK_SIZE); ++kb)
+    {
+        a_offset = ib * n * BLOCK_SIZE + kb * BLOCK_SIZE;
+        b_offset = kb * n * BLOCK_SIZE + jb * BLOCK_SIZE;
+        As[it][jt] = a[a_offset + it * n + jt];
+        Bs[it][jt] = b[b_offset + it * n + jt];
+        __syncthreads();
+
+        for (int k = 0; k < BLOCK_SIZE; ++k)
+            Cvalue += As[it][k] * Bs[k][jt];
+
+        __syncthreads();
+    }
+
+    c_offset = ib * n * BLOCK_SIZE + jb * BLOCK_SIZE;
+    c[c_offset + it * n + jt] = Cvalue;
+}
+
+int main(int argc, char *argv[])
+{
+    int n = N, iret = 0;
+    float *a, *b, *c, *g;
+    struct timespec rt[2];
+    double wt; // walltime
+
+    if (argc > 1)
+        n = atoi(argv[1]);
+
+    //TODO Update malloc to cudaMallocHost or cudaMallocManaged (if necessary)
+    if (NULL == (a = (float *)malloc(sizeof(*a) * n * n)))
+    {
+        printf("error: memory allocation for 'x'\n");
+        iret = -1;
+    }
+    //TODO Update malloc to cudaMallocHost or cudaMallocManaged (if necessary)    
+    if (NULL == (b = (float *)malloc(sizeof(*b) * n * n)))
+    {
+        printf("error: memory allocation for 'y'\n");
+        iret = -1;
+    }
+    //TODO Update malloc to cudaMallocHost or cudaMallocManaged (if necessary)    
+    if (NULL == (c = (float *)malloc(sizeof(*c) * n * n)))
+    {
+        printf("error: memory allocation for 'z'\n");
+        iret = -1;
+    }
+    if (NULL == (g = (float *)malloc(sizeof(*g) * n * n)))
+    {
+        printf("error: memory allocation for 'z'\n");
+        iret = -1;
+    }
+
+    if (0 != iret)
+    {
+        //TODO Update cudaFreeHost or cudaFree (if necessary)
+        free(a);
+        //TODO Update cudaFreeHost or cudaFree (if necessary)        
+        free(b);
+        //TODO Update cudaFreeHost or cudaFree (if necessary)        
+        free(c);
+        free(g);
+        exit(EXIT_FAILURE);
+    }
+
+    //Init Data
+    int _b = rand() % TWO04;
+    int _c = rand() % TWO08;
+
+#pragma omp parallel for
+    for (int i = 0; i < n * n; i++)
+    {
+        a[i] = _b / (float)TWO02;
+        b[i] = _c / (float)TWO04;
+        c[i] = g[i] = 0.0;
+    }
+
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    gemm_host(a, b, g, n);
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("GEMM (Host) : %9.3f sec %9.1f GFLOPS\n", wt, 2.0 * n * n * n / (1.0e9 * wt));
+
+    //TODO Remove if unecessary
+    float *d_a, *d_b, *d_c;
+    gpuErrchk(cudaMalloc((void **)&d_a, sizeof(float) * n * n));
+    gpuErrchk(cudaMalloc((void **)&d_b, sizeof(float) * n * n));
+    gpuErrchk(cudaMalloc((void **)&d_c, sizeof(float) * n * n));
+
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    //TODO Remove if unecessary
+    gpuErrchk(cudaMemcpy(d_a, a, sizeof(float) * n * n, cudaMemcpyHostToDevice));
+    gpuErrchk(cudaMemcpy(d_b, b, sizeof(float) * n * n, cudaMemcpyHostToDevice));
+    dim3 dimBlock(BLOCK_SIZE, BLOCK_SIZE);
+    dim3 dimGrid((n + (BLOCK_SIZE)-1) / (BLOCK_SIZE), (n + (BLOCK_SIZE)-1) / (BLOCK_SIZE));
+    gemm<<<dimGrid, dimBlock>>>(d_a, d_b, d_c, n);
+    gpuErrchk(cudaPeekAtLastError());
+    //TODO Remove if unecessary
+    gpuErrchk(cudaMemcpy(c, d_c, sizeof(float) * n * n, cudaMemcpyDeviceToHost));
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("GEMM-v1 (GPU): %9.3f sec %9.1f GFLOPS\n", wt, 2.0 * n * n * n / (1.0e9 * wt));
+
+    for (int i = 0; i < n * n; i++)
+    {
+        iret = *(int *)(g + i) ^ *(int *)(c + i);
+        assert(iret == 0);
+    }
+
+    //TODO Update cudaFreeHost or cudaFree (if necessary)
+    free(a);
+    //TODO Update cudaFreeHost or cudaFree (if necessary)
+    free(b);
+    //TODO Update cudaFreeHost or cudaFree (if necessary)
+    free(c);
+    free(g);
+    //TODO Remove if unecessary
+    gpuErrchk(cudaFree(d_a));
+    //TODO Remove if unecessary
+    gpuErrchk(cudaFree(d_b));
+    //TODO Remove if unecessary
+    gpuErrchk(cudaFree(d_c));
+
+    return 0;
+}
diff --git a/cuda/appendix/saxpy/saxpy.cu b/cuda/appendix/saxpy/saxpy.cu
new file mode 100644
index 0000000..578b131
--- /dev/null
+++ b/cuda/appendix/saxpy/saxpy.cu
@@ -0,0 +1,183 @@
+/*
+ * BSD 2-Clause License
+ * 
+ * Copyright (c) 2020, Alessandro Capotondi
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ * 
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @file saxpy.c
+ * @author Alessandro Capotondi
+ * @date 12 May 2020
+ * @brief Saxpy
+ * 
+ * @see https://dolly.fim.unimore.it/2019/course/view.php?id=152
+ */
+
+#include <assert.h>
+#include <time.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+#include <cuda_runtime.h>
+
+#define gpuErrchk(ans)                        \
+    {                                         \
+        gpuAssert((ans), __FILE__, __LINE__); \
+    }
+static inline void gpuAssert(cudaError_t code, const char *file, int line, bool abort = true)
+{
+    if (code != cudaSuccess)
+    {
+        fprintf(stderr, "GPUassert: %s %s %d\n", cudaGetErrorString(code), file, line);
+        if (abort)
+            exit(code);
+    }
+}
+
+#define TWO02 (1 << 2)
+#define TWO04 (1 << 4)
+#define TWO08 (1 << 8)
+#ifndef N
+#define N (1 << 27)
+#endif
+
+#ifndef BLOCK_SIZE
+#define BLOCK_SIZE (512)
+#endif
+
+/*
+ *SAXPY (host implementation)
+ * y := a * x + y
+ */
+void host_saxpy(float * __restrict__ y, float a, float * __restrict__ x, int n)
+{
+#pragma omp parallel for simd schedule(simd: static)
+    for (int i = 0; i < n; i++)
+    {
+        y[i] = a * x[i] + y[i];
+    }
+}
+
+__global__ void gpu_saxpy(float * __restrict__ y, float a, float * __restrict__ x, int n)
+{
+    int i = blockIdx.x * blockDim.x + threadIdx.x;
+    if (i < n)
+        y[i] = a * x[i] + y[i];
+}
+
+int main(int argc, const char **argv)
+{
+    int iret = 0;
+    int n = N;
+    float *h_x, *d_x;
+    float *h_y, *d_y;
+    float *h_z;
+    float a = 101.0f / TWO02,
+          b, c;
+    struct timespec rt[2];
+    double wt; // walltime
+
+    if (argc > 1)
+        n = atoi(argv[1]);
+
+    //TODO Update malloc to cudaMallocHost or cudaMallocManaged (if necessary)
+    if (NULL == (h_x = (float *)malloc(sizeof(float) * n)))
+    {
+        printf("error: memory allocation for 'x'\n");
+        iret = -1;
+    }
+    //TODO Update malloc to cudaMallocHost or cudaMallocManaged (if necessary)
+    if (NULL == (h_y = (float *)malloc(sizeof(float) * n)))
+    {
+        printf("error: memory allocation for 'y'\n");
+        iret = -1;
+    }
+    if (NULL == (h_z = (float *)malloc(sizeof(float) * n)))
+    {
+        printf("error: memory allocation for 'z'\n");
+        iret = -1;
+    }
+    if (0 != iret)
+    {
+        //TODO Update cudaFreeHost or cudaFree (if necessary)
+        free(h_x);
+        //TODO Update cudaFreeHost or cudaFree (if necessary)
+        free(h_y);
+        free(h_z);
+        exit(EXIT_FAILURE);
+    }
+
+    //Init Data
+    b = rand() % TWO04;
+    c = rand() % TWO08;
+    for (int i = 0; i < n; i++)
+    {
+        h_x[i] = b / (float)TWO02;
+        h_y[i] = h_z[i] = c / (float)TWO04;
+    }
+
+    //TODO Remove if unecessary
+    gpuErrchk(cudaMalloc((void **)&d_x, sizeof(float) * n));
+    gpuErrchk(cudaMalloc((void **)&d_y, sizeof(float) * n));
+
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    //TODO Remove if unecessary
+    gpuErrchk(cudaMemcpy(d_x, h_x, sizeof(float) * n, cudaMemcpyHostToDevice));
+    gpuErrchk(cudaMemcpy(d_y, h_y, sizeof(float) * n, cudaMemcpyHostToDevice));
+    gpu_saxpy<<<((n + BLOCK_SIZE - 1) / BLOCK_SIZE), BLOCK_SIZE>>>(d_y, a, d_x, n);
+    gpuErrchk(cudaPeekAtLastError());
+    //TODO Remove if unecessary
+    gpuErrchk(cudaMemcpy(h_y, d_y, sizeof(float) * n, cudaMemcpyDeviceToHost));
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("saxpy (GPU): %9.3f sec %9.1f GFLOPS\n", wt, 2 * n / wt);
+
+    //Check Matematical Consistency
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    host_saxpy(h_z, a, h_x, n);
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("saxpy (Host): %9.3f sec %9.1f GFLOPS\n", wt, 2 * n / wt);
+    for (int i = 0; i < n; ++i)
+    {
+        iret = *(int *)(h_y + i) ^ *(int *)(h_z + i);
+        assert(iret == 0);
+    }
+
+    //TODO Update cudaFreeHost or cudaFree (if necessary)
+    free(h_x);
+    //TODO Remove if unecessary
+    gpuErrchk(cudaFree(d_x));
+    //TODO Update cudaFreeHost or cudaFree (if necessary)
+    free(h_y);
+    //TODO Remove if unecessary
+    gpuErrchk(cudaFree(d_y));
+    free(h_z);
+
+    // CUDA exit -- needed to flush printf write buffer
+    cudaDeviceReset();
+    return 0;
+}
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diff --git a/cuda/appendix/sobel/data/earth_rise.jpg b/cuda/appendix/sobel/data/earth_rise.jpg
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diff --git a/cuda/appendix/sobel/data/fiore.jpg b/cuda/appendix/sobel/data/fiore.jpg
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diff --git a/cuda/appendix/sobel/sobel.cu b/cuda/appendix/sobel/sobel.cu
new file mode 100644
index 0000000..ad3d0e5
--- /dev/null
+++ b/cuda/appendix/sobel/sobel.cu
@@ -0,0 +1,361 @@
+/*
+ * BSD 2-Clause License
+ * 
+ * Copyright (c) 2020, Alessandro Capotondi
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ * 
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @file sobel.cu
+ * @author Alessandro Capotondi
+ * @date 5 May 2020
+ * @brief Stencil 2d - Sobel
+ * 
+ * @see https://dolly.fim.unimore.it/2019/course/view.php?id=152
+ */
+
+#include <stdio.h>
+#include <time.h>
+#include <sys/time.h>
+#include <opencv2/opencv.hpp>
+#include <opencv2/imgcodecs/imgcodecs.hpp>
+#include <opencv2/objdetect/objdetect.hpp>
+#include <opencv2/highgui/highgui.hpp>
+
+using namespace cv;
+using namespace std;
+
+#ifndef BLOCK_SIZE
+#define BLOCK_SIZE 32
+#endif
+
+#define gpuErrchk(ans)                        \
+    {                                         \
+        gpuAssert((ans), __FILE__, __LINE__); \
+    }
+static inline void gpuAssert(cudaError_t code, const char *file, int line, bool abort = true)
+{
+    if (code != cudaSuccess)
+    {
+        fprintf(stderr, "GPUassert: %s %s %d\n", cudaGetErrorString(code), file, line);
+        if (abort)
+            exit(code);
+    }
+}
+
+void sobel_host(unsigned char *__restrict__ orig, unsigned char *__restrict__ out, int width, int height)
+{
+#pragma omp parallel for simd collapse(2)
+    for (int y = 1; y < height - 1; y++)
+    {
+        for (int x = 1; x < width - 1; x++)
+        {
+            int dx = (-1 * orig[(y - 1) * width + (x - 1)]) + (-2 * orig[y * width + (x - 1)]) + (-1 * orig[(y + 1) * width + (x - 1)]) +
+                     (orig[(y - 1) * width + (x + 1)]) + (2 * orig[y * width + (x + 1)]) + (orig[(y + 1) * width + (x + 1)]);
+            int dy = (orig[(y - 1) * width + (x - 1)]) + (2 * orig[(y - 1) * width + x]) + (orig[(y - 1) * width + (x + 1)]) +
+                     (-1 * orig[(y + 1) * width + (x - 1)]) + (-2 * orig[(y + 1) * width + x]) + (-1 * orig[(y + 1) * width + (x + 1)]);
+            out[y * width + x] = sqrt((float)((dx * dx) + (dy * dy)));
+        }
+    }
+}
+
+__global__ void sobel_v1(unsigned char *__restrict__ orig, unsigned char *__restrict__ out, int width, int height)
+{
+    int i = threadIdx.y + blockIdx.y * blockDim.y;
+    int j = threadIdx.x + blockIdx.x * blockDim.x;
+
+    if (j > 0 && i > 0 && j < width - 1 && i < height - 1)
+    {
+        int dx = (-1 * orig[(i - 1) * width + (j - 1)]) + (-2 * orig[i * width + (j - 1)]) + (-1 * orig[(i + 1) * width + (j - 1)]) +
+                 (orig[(i - 1) * width + (j + 1)]) + (2 * orig[i * width + (j + 1)]) + (orig[(i + 1) * width + (j + 1)]);
+        int dy = (orig[(i - 1) * width + (j - 1)]) + (2 * orig[(i - 1) * width + j]) + (orig[(i - 1) * width + (j + 1)]) +
+                 (-1 * orig[(i + 1) * width + (j - 1)]) + (-2 * orig[(i + 1) * width + j]) + (-1 * orig[(i + 1) * width + (j + 1)]);
+        out[i * width + j] = sqrt((float)((dx * dx) + (dy * dy)));
+    }
+}
+
+__global__ void sobel_v2(unsigned char *__restrict__ orig, unsigned char *__restrict__ out, int width, int height)
+{
+    //TODO Declare i and j: global output indexes
+    int i = threadIdx.y + blockIdx.y * blockDim.y;
+    int j = threadIdx.x + blockIdx.x * blockDim.x;
+
+    //TODO Declare it and jt: Thread row and column of output matrix
+    int it = threadIdx.y;
+    int jt = threadIdx.x;
+
+    //TODO Declare shared input patch
+    __shared__ unsigned char s_in[BLOCK_SIZE][BLOCK_SIZE];
+
+    //TODO Load input patch
+    // Each thread loads one element of the patch
+    s_in[it][jt] = orig[i * width + j];
+
+    //TODO Synchronize to make sure the sub-matrices are loaded
+    // before starting the computation
+    __syncthreads();
+
+    //TODO if block boundary do
+    if (jt > 0 && it > 0 && jt < BLOCK_SIZE - 1 && it < BLOCK_SIZE - 1 && j > 0 && i > 0 && j < width - 1 && i < height - 1)
+    {
+        int dx = (-1 * s_in[it - 1][jt - 1]) + (-2 * s_in[it][jt - 1]) + (-1 * s_in[it + 1][jt - 1]) +
+                 (s_in[it - 1][jt + 1]) + (2 * s_in[it][jt + 1]) + (s_in[it + 1][jt + 1]);
+        int dy = (s_in[it - 1][jt - 1]) + (2 * s_in[it - 1][jt]) + (s_in[it - 1][jt + 1]) +
+                 (-1 * s_in[it + 1][jt - 1]) + (-2 * s_in[it + 1][jt]) + (-1 * s_in[it + 1][jt + 1]);
+        out[i * width + j] = sqrt((float)((dx * dx) + (dy * dy)));
+    }
+    else if (j > 0 && i > 0 && j < width - 1 && i < height - 1)
+    {
+        //TODO if not-block boundary do (tip check global boundaries)
+        int dx = (-1 * orig[(i - 1) * width + (j - 1)]) + (-2 * orig[i * width + (j - 1)]) + (-1 * orig[(i + 1) * width + (j - 1)]) +
+                 (orig[(i - 1) * width + (j + 1)]) + (2 * orig[i * width + (j + 1)]) + (orig[(i + 1) * width + (j + 1)]);
+        int dy = (orig[(i - 1) * width + (j - 1)]) + (2 * orig[(i - 1) * width + j]) + (orig[(i - 1) * width + (j + 1)]) +
+                 (-1 * orig[(i + 1) * width + (j - 1)]) + (-2 * orig[(i + 1) * width + j]) + (-1 * orig[(i + 1) * width + (j + 1)]);
+        out[i * width + j] = sqrt((float)((dx * dx) + (dy * dy)));
+    }
+}
+
+__global__ void sobel_v3(unsigned char *__restrict__ orig, unsigned char *__restrict__ out, int width, int height)
+{
+    //TODO Declare i and j: global output indexes (tip: use BLOCK_SIZE-2)
+    int i = threadIdx.y + blockIdx.y * (BLOCK_SIZE - 2);
+    int j = threadIdx.x + blockIdx.x * (BLOCK_SIZE - 2);
+
+    //TODO Declare it and jt: Thread row and column of output matrix
+    int it = threadIdx.y;
+    int jt = threadIdx.x;
+
+    //TODO Check if i and j are out of memory
+    if (i >= width && j >= height)
+        return;
+
+    //TODO Declare shared input patch
+    __shared__ unsigned char s_in[BLOCK_SIZE][BLOCK_SIZE];
+
+    //TODO Load input patch
+    // Each thread loads one element of the patch
+    s_in[it][jt] = orig[i * width + j];
+
+    //TODO Synchronize to make sure the sub-matrices are loaded
+    // before starting the computation
+    __syncthreads();
+
+    //TODO Update block and bound checks
+    if (jt > 0 && it > 0 && jt < BLOCK_SIZE - 1 && it < BLOCK_SIZE - 1 && j > 0 && i > 0 && j < width - 1 && i < height - 1)
+    {
+        int dx = (-1 * s_in[it - 1][jt - 1]) + (-2 * s_in[it][jt - 1]) + (-1 * s_in[it + 1][jt - 1]) +
+                 (s_in[it - 1][jt + 1]) + (2 * s_in[it][jt + 1]) + (s_in[it + 1][jt + 1]);
+        int dy = (s_in[it - 1][jt - 1]) + (2 * s_in[it - 1][jt]) + (s_in[it - 1][jt + 1]) +
+                 (-1 * s_in[it + 1][jt - 1]) + (-2 * s_in[it + 1][jt]) + (-1 * s_in[it + 1][jt + 1]);
+        out[i * width + j] = sqrt((float)((dx * dx) + (dy * dy)));
+    }
+}
+
+__global__ void sobel_v4(unsigned char *__restrict__ orig, unsigned char *__restrict__ out, int width, int height)
+{
+    //TODO Declare i and j: global output indexes (tip: use BLOCK_SIZE)
+    int i = threadIdx.y + blockIdx.y * blockDim.y;
+    int j = threadIdx.x + blockIdx.x * blockDim.x;
+
+    //TODO Declare it and jt: Thread row and column of output matrix
+    int it = threadIdx.y;
+    int jt = threadIdx.x;
+
+    //TODO Declare shared input patch (tip: use BLOCK_SIZE+2)
+    __shared__ unsigned char s_in[BLOCK_SIZE + 32][BLOCK_SIZE + 32];
+
+    //TODO Load input patch
+    // Each thread loads one element of the patch
+    s_in[it][jt] = orig[i * width + j];
+
+    //TODO Check condition and load remaining elements
+    if ((it + BLOCK_SIZE) < BLOCK_SIZE + 2 && (jt) < BLOCK_SIZE + 2 && (i + BLOCK_SIZE) < width && (j) < height)
+        s_in[it + BLOCK_SIZE][jt] = orig[(i + BLOCK_SIZE) * width + j];
+
+    if ((it) < BLOCK_SIZE + 2 && (jt + BLOCK_SIZE) < BLOCK_SIZE + 2 && (i) < width && (j + BLOCK_SIZE) < height)
+        s_in[it][jt + BLOCK_SIZE] = orig[i * width + j + BLOCK_SIZE];
+
+    if ((it + BLOCK_SIZE) < BLOCK_SIZE + 2 && (jt + BLOCK_SIZE) < BLOCK_SIZE + 2 && (i + BLOCK_SIZE) < width && (j + BLOCK_SIZE) < height)
+        s_in[it + BLOCK_SIZE][jt + BLOCK_SIZE] = orig[(i + BLOCK_SIZE) * width + j + BLOCK_SIZE];
+
+    //TODO Synchronize to make sure the sub-matrices are loaded
+    // before starting the computation
+    __syncthreads();
+
+    //TODO Update all idx adding y +1 and x +1
+    if (jt < BLOCK_SIZE && it < BLOCK_SIZE && j < (width - 2) && i < (height - 2))
+    {
+        int dx = (-1 * s_in[it - 1 + 1][jt - 1 + 1]) + (-2 * s_in[it + 1][jt - 1 + 1]) + (-1 * s_in[it + 1 + 1][jt - 1 + 1]) +
+                 (s_in[it - 1 + 1][jt + 1 + 1]) + (2 * s_in[it + 1][jt + 1 + 1]) + (s_in[it + 1 + 1][jt + 1 + 1]);
+        int dy = (s_in[it - 1 + 1][jt - 1 + 1]) + (2 * s_in[it - 1 + 1][jt + 1]) + (s_in[it - 1 + 1][jt + 1 + 1]) +
+                 (-1 * s_in[it + 1 + 1][jt - 1 + 1]) + (-2 * s_in[it + 1 + 1][jt + 1]) + (-1 * s_in[it + 1 + 1][jt + 1 + 1]);
+        out[(i + 1) * width + j + 1] = sqrt((float)((dx * dx) + (dy * dy)));
+    }
+}
+
+int main(int argc, char *argv[])
+{
+    int iret = 0;
+    struct timespec rt[2];
+    double wt; // walltime
+    string filename("../data/buzz.jpg");
+
+    if (argc > 1)
+        filename = argv[1];
+
+    // Load Image
+    Mat image = imread(filename, IMREAD_GRAYSCALE);
+    if (!image.data)
+    {
+        cout << "Could not open or find the image" << std::endl;
+        return -1;
+    }
+    int width = image.size().width;
+    int height = image.size().height;
+
+    // Create Output Images
+    Mat out1 = image.clone();
+    Mat out2 = image.clone();
+    Mat result = image.clone();
+    memset(out1.ptr(), 0, sizeof(unsigned char) * width * height);
+    memset(out2.ptr(), 0, sizeof(unsigned char) * width * height);
+    memset(result.ptr(), 0, sizeof(unsigned char) * width * height);
+
+    // Compute CPU Version - Golden Model
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    sobel_host(image.ptr(), out1.ptr(), width, height);
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("Sobel (Host) : %9.6f sec\n", wt);
+
+    //CUDA Buffer Allocation
+    unsigned char *d_image_in;
+    unsigned char *d_image_out;
+    gpuErrchk(cudaMalloc((void **)&d_image_in, sizeof(unsigned char) * width * height));
+    gpuErrchk(cudaMalloc((void **)&d_image_out, sizeof(unsigned char) * width * height));
+    gpuErrchk(cudaMemset(d_image_out, 0, sizeof(unsigned char) * width * height));
+
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    gpuErrchk(cudaMemcpy(d_image_in, image.ptr(), sizeof(unsigned char) * width * height, cudaMemcpyHostToDevice));
+    dim3 dimBlock(BLOCK_SIZE, BLOCK_SIZE);
+    dim3 dimGrid((width + BLOCK_SIZE - 1) / BLOCK_SIZE, (height + BLOCK_SIZE - 1) / BLOCK_SIZE);
+    sobel_v1<<<dimGrid, dimBlock>>>(d_image_in, d_image_out, width, height);
+    gpuErrchk(cudaPeekAtLastError());
+    gpuErrchk(cudaMemcpy(out2.ptr(), d_image_out, sizeof(unsigned char) * width * height, cudaMemcpyDeviceToHost));
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("Sobel-v1 (GPU) : %9.6f sec\n", wt);
+
+    //Check results
+    absdiff(out1, out2, result);
+    int percentage = countNonZero(result);
+
+    //Reset Output image
+    memset(out2.ptr(), 0, sizeof(unsigned char) * width * height);
+    gpuErrchk(cudaMemset(d_image_out, 0, sizeof(unsigned char) * width * height));
+
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    gpuErrchk(cudaMemcpy(d_image_in, image.ptr(), sizeof(unsigned char) * width * height, cudaMemcpyHostToDevice));
+    // dim3 dimBlock(BLOCK_SIZE, BLOCK_SIZE);
+    // dim3 dimGrid((width + BLOCK_SIZE - 1) / BLOCK_SIZE, (height + BLOCK_SIZE - 1) / BLOCK_SIZE);
+    sobel_v2<<<dimGrid, dimBlock>>>(d_image_in, d_image_out, width, height);
+    gpuErrchk(cudaPeekAtLastError());
+    gpuErrchk(cudaMemcpy(out2.ptr(), d_image_out, sizeof(unsigned char) * width * height, cudaMemcpyDeviceToHost));
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("Sobel-v2 (GPU) : %9.6f sec\n", wt);
+
+    //Check results
+    absdiff(out1, out2, result);
+    percentage = countNonZero(result);
+    if (percentage)
+    {
+        printf("Divergence %d\n", percentage);
+        imshow("Output GPU", out2);
+        imshow("error diff", result);
+        waitKey(0);
+    }
+    assert(percentage == 0);
+
+    //Reset Output image
+    memset(out2.ptr(), 0, sizeof(unsigned char) * width * height);
+    gpuErrchk(cudaMemset(d_image_out, 0, sizeof(unsigned char) * width * height));
+
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    gpuErrchk(cudaMemcpy(d_image_in, image.ptr(), sizeof(unsigned char) * width * height, cudaMemcpyHostToDevice));
+    //TODO define dimGrid, dimBlock
+    //TODO add sobel_v4 call
+    dim3 dimBlock_v3(BLOCK_SIZE, BLOCK_SIZE);
+    dim3 dimGrid_v3((width + (BLOCK_SIZE - 2) - 1) / (BLOCK_SIZE - 2), (height + (BLOCK_SIZE - 2) - 1) / (BLOCK_SIZE - 2));
+    sobel_v3<<<dimGrid_v3, dimBlock_v3>>>(d_image_in, d_image_out, width, height);
+    gpuErrchk(cudaPeekAtLastError());
+    gpuErrchk(cudaMemcpy(out2.ptr(), d_image_out, sizeof(unsigned char) * width * height, cudaMemcpyDeviceToHost));
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("Sobel-v3 (GPU) : %9.6f sec\n", wt);
+
+    //Check results
+    absdiff(out1, out2, result);
+    percentage = countNonZero(result);
+    if (percentage)
+    {
+        printf("Divergence %d\n", percentage);
+        imshow("Output GPU", out2);
+        imshow("error diff", result);
+        waitKey(0);
+    }
+    assert(percentage == 0);
+
+    //Reset Output image
+    memset(out2.ptr(), 0, sizeof(unsigned char) * width * height);
+    gpuErrchk(cudaMemset(d_image_out, 0, sizeof(unsigned char) * width * height));
+
+    clock_gettime(CLOCK_REALTIME, rt + 0);
+    gpuErrchk(cudaMemcpy(d_image_in, image.ptr(), sizeof(unsigned char) * width * height, cudaMemcpyHostToDevice));
+    //TODO define dimGrid, dimBlock
+    //TODO add sobel_v4 call
+    sobel_v4<<<dimGrid, dimBlock>>>(d_image_in, d_image_out, width, height);
+    gpuErrchk(cudaPeekAtLastError());
+    gpuErrchk(cudaMemcpy(out2.ptr(), d_image_out, sizeof(unsigned char) * width * height, cudaMemcpyDeviceToHost));
+    clock_gettime(CLOCK_REALTIME, rt + 1);
+    wt = (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
+    printf("Sobel-v4 (GPU) : %9.6f sec\n", wt);
+
+    //Check results
+    absdiff(out1, out2, result);
+    percentage = countNonZero(result);
+    if (percentage)
+    {
+        printf("Divergence %d\n", percentage);
+        imshow("Output GPU", out2);
+        imshow("error diff", result);
+        waitKey(0);
+    }
+    assert(percentage == 0);
+
+    gpuErrchk(cudaFree(d_image_out));
+    gpuErrchk(cudaFree(d_image_in));
+
+    return iret;
+}