Help with matrices

[craziileeboi]

Can anyone tell me why the mult_matrix isnt working correctly? ignore extra text, this is a small section of a larger assignment... I'm stuck and any help would be appreciated thanks

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#define ROWA 4
#define COLA 4
 
void prob1(void);
void prob2(void);
double unit_norm(double vec[4], int cols);
void matrix_mult(double a[4][4],double b[4], double c[4], int rows);
double unit_vec(double vec[4], int cols);
double pmatrix(double **A, double **B, double *a, double *b, int n);
 
 
 
 
double a[4][4], b[4], c[4];
int n=4,t,  row, rows, col, cols, k;
 
main()
{
        int menu;
        printf("Enter the function number to execute (1-2):");
        scanf("%d", &menu);
        switch(menu){
         case 1:
            prob1();
            break;
         case 2:
            prob2();
            break;
         default:
            printf("prob%d() does not exist.\n", menu);
        }
        exit(0);
}
 
 
void prob1(void)
{
double K[4][4] = { { 2., -4.,  1.,  0.},
                    {-4.,  5., -2.,  1.},
                    { 1., -2.,  6., -3.},
                    { 0.,  1., -3.,  7.}};
double y[4], x[4] = { 1./3., 2./3., 1./3., pow(3.,0.5)/3.};
int k, rows, i;
double dot_p;
 
 
printf("\nInitial vector:\n");
printf("x[0] = [" );
for(rows=0; rows<4; rows++){
        printf(" %f", x[rows]);
        }
printf("]\n");
printf("\nNew Vector:\n");
for(t=0; t<10; t++){
        printf("y[%d] = [", t);
        for(rows = 0; rows<4; rows++){
               // printf(" %g", matrix_mult(double a[4][4], double b[4], double c[4], int row));
        }
        printf("]\n");
}
}
 
 
void matrix_mult(double a[4][4], double b[4], double c[4], int row)
{
/* compute c[]=a[][]*b[]*/
int col;
double sum;
for(row=0;row<4; row++){
        for(col=0, sum=0.0;col<4; col++){
                sum +=a[row][col]*b[col];
                }
        c[row]=sum;
        }
return;
}
 
double unit_norm(double vec[4], int cols)
{
double sum=0;
/* normalize a vector */
int i;
for(i=0; i<cols; i++)
        sum += vec[i] * vec[i];
sum = sqrt(sum);
for(i=0; i<cols; i++)
vec[i]=vec[i]/sum;
return sum;
}

[RRick]

Before we can help you, you need to tell us what and where the problem is.

If your problem is in the printf statement (line 60) with matrix_mult, then that is not going to work. You need to pass existing arrays to matrix_mult, and then you can print out the result (i.e. c array) in the loop with the printf statement. Since matrix_mult does not return anything, you can't use it in the printf statement.

[craziileeboi]

its okay i got THIS program to work but if you can check my other thread or post, that would be great.