matrix_sigmoid.cu

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/**
 * @file matrix_sigmoid.cu
 * @brief Implementation of the sigmoid activation function for matrices.
 */
 
#include "matrix.h"
#include <cuda_runtime.h>
#include <math.h>
 
/**
 * @brief CUDA kernel for applying the sigmoid activation function element-wise.
 * @param input Pointer to the input matrix data.
 * @param output Pointer to the output matrix data.
 * @param size Total number of elements in the matrix.
 */
__global__ void sigmoidKernel(const double* input, double* output, int size) {
    // Calculate the global thread index
    int idx = blockIdx.x * blockDim.x + threadIdx.x;
    
    // Check if the thread is within the matrix bounds
    if (idx < size) {
        // Apply sigmoid: 1 / (1 + exp(-x))
        output[idx] = 1.0 / (1.0 + exp(-input[idx]));
    }
}
 
/**
 * @brief Applies the sigmoid activation function to the matrix.
 * @return A new Matrix object with sigmoid applied.
 */
Matrix Matrix::sigmoid() const {
    // Create a new matrix with the same dimensions
    Matrix result(rows, cols);
    
    // Calculate the total number of elements
    int size = rows * cols;
    
    // Define the number of threads per block
    int threadsPerBlock = 256;
    
    // Calculate the number of blocks needed
    int blocksPerGrid = (size + threadsPerBlock - 1) / threadsPerBlock;
    
    // Launch the CUDA kernel
    sigmoidKernel<<<blocksPerGrid, threadsPerBlock>>>(d_data, result.d_data, size);
    
    // Synchronize to ensure the kernel execution is complete
    cudaDeviceSynchronize();
    
    return result;
}