Math.lab1

#include <stdio.h>
#include <stdlib.h>
#define MAXSIZE 4

int read_matrix(char *file_name, float matrix[][MAXSIZE]);
void print_matrix(int size, float matrix[][MAXSIZE]);
void great_diagonal(int size, float matrix[][MAXSIZE]);
void swap_rows(int master, int slave, int size, float matrix[][MAXSIZE]);
void triangle_matrix(int size, float matrix[][MAXSIZE]);
void upward(int size, float matrix[][MAXSIZE]);

int main(int argc, char *argv[])
{
    char *file_name = "input";
    float matrix[MAXSIZE][MAXSIZE];
    int size = 0;

    size = read_matrix(file_name, matrix);
    printf("\nOriginal matrix:\n");
    print_matrix(size, matrix);
    great_diagonal(size, matrix);
    printf("Matrix with selection of main value in columns\n");
    print_matrix(size, matrix);
    triangle_matrix(size, matrix);
    printf("Triangle matrix:\n");
    print_matrix(size, matrix);
    upward(size, matrix);

    return 0;
}

void triangle_matrix(int size, float matrix[][MAXSIZE])
{
    int i, j, k;
    float factor_master, factor_slave;

    for (k = 0; k < size; k++) {
        if (abs(matrix[k][k]) == 0) {
            swap_rows(k+1, k, size, matrix);
            printf("after 0-swap:\n");
            print_matrix(size, matrix);
        }
        factor_master = matrix[k][k];
        for (j = k; j < size+1; j++) {
            matrix[k][j] = matrix[k][j] / factor_master;
        }

        for (i = k+1; i < size; i++) {
            factor_slave = matrix[i][k];
            for (j = 0; j < size+1; j++) {
                matrix[i][j] = matrix[i][j] - matrix[k][j] * factor_slave;
            }
        }
        printf("step #%d\n", k+1);
        print_matrix(size, matrix);
    }
}

void upward(int size, float matrix[][MAXSIZE])
{
    int i, j;
    float x[size-1], tmp;

    x[0] = matrix[size-1][size];

    for (i = 1; i >= 0; i--) {
        tmp = 0.0;
        for (j = 0; j < size-i-1; j++)
            tmp -= matrix[i][size-j-1] * x[j];
        tmp += matrix[i][size];
        x[size-i-1] = tmp;
    }

    putchar('\n');
    for (i = 0; i < size; i++)
        printf("x%d = %11f\n", i+1, x[size-i-1]);

}

void great_diagonal(int size, float matrix[][MAXSIZE])
{
    int i, j, max_indx;
    float max;

    for (j = 0; j < size; j++) {
        max = 0;
        max_indx = 0;
        for (i = j; i < size; i++) {
            if (abs(matrix[i][j]) > abs(max)) {
                max = matrix[i][j];
                max_indx = i;
            }
        }
        if (abs(matrix[max_indx][j]) > abs(matrix[j][j])) {
            swap_rows(max_indx, j, size, matrix);
        }
    }
}

void swap_rows(int master, int slave, int size, float matrix[][MAXSIZE])
{
    int j;
    float temp = 0;

    for (j = 0; j < size+1; j++) {
        temp = matrix[slave][j];
        matrix[slave][j] = matrix[master][j];
        matrix[master][j] = temp;
    }
}

int read_matrix(char *file_name, float matrix[][MAXSIZE])
{
    FILE *ifp;
    int i, j, size = 0;

    ifp = fopen(file_name, "r");
    fscanf(ifp, "%d", &size);
    for (i = 0; i < size; i++) {
        for (j = 0; j < size+1; j++) {
            fscanf(ifp, "%f", &matrix[i][j]);
        }
    }
    fclose(ifp);

    return size;
}

void print_matrix(int size, float matrix[][MAXSIZE])
{
    int i, j;

    putchar('\n');
    for (i = 0; i < size; i++) {
        for (j = 0; j < size+1; j++) {
            printf("%16f", matrix[i][j]);
        }
        putchar('\n');
    }
    putchar('\n');
}