Lecture 145:- Let's Code Lower Triangular Matrix in C

Below is the C implementation of a lower triangular matrix using a 1D array and row-major mapping:

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#include <stdio.h> #include <stdlib.h> struct LowerTriangularMatrix {    int size; // Size of the matrix    int* elements; // 1D array to store diagonal elements }; // Function to create a lower triangular matrix of given size struct LowerTriangularMatrix* createLowerTriangularMatrix(int n) {    struct LowerTriangularMatrix* matrix = (struct LowerTriangularMatrix*)malloc(sizeof(struct LowerTriangularMatrix));    matrix->size = n;    int totalElements = n * (n + 1) / 2;    matrix->elements = (int*)calloc(totalElements, sizeof(int));    return matrix; } // Function to set an element at (i, j) position in the lower triangular matrix void setElement(struct LowerTriangularMatrix* matrix, int i, int j, int value) {    if (i >= j && i < matrix->size && j < matrix->size) {        int index = i * (i + 1) / 2 + j;        matrix->elements[index] = value;    } else {        printf("Invalid index. Element not set.\n");    } } // Function to get an element from (i, j) position in the lower triangular matrix int getElement(struct LowerTriangularMatrix* matrix, int i, int j) {    if (i >= j && i < matrix->size && j < matrix->size) {        int index = i * (i + 1) / 2 + j;        return matrix->elements[index];    } else {        printf("Invalid index. Returning 0.\n");        return 0;    } } // Function to display the lower triangular matrix void displayLowerTriangularMatrix(struct LowerTriangularMatrix* matrix) {    printf("Lower Triangular Matrix:\n");    for (int i = 0; i < matrix->size; i++) {        for (int j = 0; j < matrix->size; j++) {            if (i >= j) {                int index = i * (i + 1) / 2 + j;                printf("%d ", matrix->elements[index]);            } else {                printf("0 ");            }        }        printf("\n");    } } // Function to deallocate memory used by the lower triangular matrix void freeLowerTriangularMatrix(struct LowerTriangularMatrix* matrix) {    free(matrix->elements);    free(matrix); } int main() {    int size = 4;    struct LowerTriangularMatrix* matrix = createLowerTriangularMatrix(size);    setElement(matrix, 0, 0, 1);    setElement(matrix, 1, 0, 2);    setElement(matrix, 1, 1, 3);    setElement(matrix, 2, 0, 4);    setElement(matrix, 2, 1, 5);    setElement(matrix, 2, 2, 6);    setElement(matrix, 3, 0, 7);    setElement(matrix, 3, 1, 8);    setElement(matrix, 3, 2, 9);    setElement(matrix, 3, 3, 10);    displayLowerTriangularMatrix(matrix);    freeLowerTriangularMatrix(matrix);    return 0; }

Output:

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Lower Triangular Matrix: 1 0 0 0 2 3 0 0 4 5 6 0 7 8 9 10

In this C code, we have defined a structure LowerTriangularMatrix, which represents a lower triangular matrix. The structure contains a size variable to store the size of the matrix and an integer pointer elements to dynamically allocate memory for the 1D array to store the matrix elements.

We create functions to create the lower triangular matrix, set and get elements at specified indices, display the matrix, and free the memory when it is no longer needed.

The main function demonstrates the usage of these functions to create, set, and display the lower triangular matrix. Finally, we deallocate the memory used by the matrix using the freeLowerTriangularMatrix function to avoid memory leaks.