problems with functions

[Xavi Camps]

I have problems using my augmented_matrix function in my gauss function.. can anybody help me?

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
double inverse(int r, int c, int* matrix[]);
int **matrix_augmented(int *a[], int *v, int r, int c);
void gauss(int r, int c, int *a[]);


int main()
{
	srand(time(NULL));
	int r;
	int c;
	printf("define the size of the matrix\n number of rows\n");
	scanf_s("%d", &r);
	printf("number of columns\n");
	scanf_s("%d", &c);
	int **matrix = (int**)malloc(r * sizeof(*matrix));
	int* vector = (int*)malloc(r*sizeof(*vector));
	for (int i = 0; i < r; i++)
	{
		matrix[i] = (int*)malloc(c * sizeof(*matrix[r]));


	}
	
	matrix_augmented(matrix, vector, r, c);
	inverse(r, c, matrix);
	gauss(r, c, matrix_augmented(matrix, vector, r, c));


	
	




}
	
	






double inverse(int r, int c, int* matrix[])
{




	double determinant = 0;
	for (int i = 0; i<r; i++)
		determinant = determinant + (matrix[0][i] * (matrix[1][(i + 1) % r] * matrix[2][(i + 2) % r] - matrix[1][(i + 2) % r] * matrix[2][(i + 1) % r]));


	printf("\nInverse of matrix is: \n\n");
	for (int j = 0; j<r; j++){
		for (int i = 0; i<r; i++)


			printf("%.4f\t", (((matrix[(i + 1) % r][(j + 1) % r] * matrix[(i + 2) % r][(j + 2) % r]) - (matrix[(i + 1) % r][(j + 2) % r] * matrix[(i + 2) % r][(j + 1) % r])) / determinant));
		printf("\n");


	}
	return (0);
}
int **matrix_augmented(int *a[], int *v, int r, int c)
{
	for (int i = 0; i < r; ++i)
	{
		for (int j = 0; j < c; ++j)
		{
			a[i][j] = rand() % 21 - 10;
			printf("%d     ", a[i][j]);
			v[i] = rand() % 21 - 10;




		}
		printf("%d", v[i]);
		printf("\n");
	}
	return 0;


}




void gauss(int r, int c, int *a[])
{
		for (int k = 0; k<r - 1; k++)
		{
			for (int i = k + 1; i<r; i++)
			{
				double p = a[i][k] / a[k][k];
				for (int j = k; j<r + 1; j++)
					a[i][j] = a[i][j] - p*a[k][j];
			}
		}
		double *x = (double*)malloc(r * sizeof(*x));


		x[r - 1] = a[r - 1][r] / a[r - 1][r - 1];
		for (int i = r - 2; i >= 0; i--)
		{
			int s = 0;
			for (int j = i + 1; j<r; j++)
			{
				s += (a[i][j] * x[j]);
				x[i] = (a[i][r] - s) / a[i][i];
			}
		}
		printf("\nThe result is:\n");
		for (int i = 0; i<r; i++)
			printf("\nx%d=%lf", i + 1, x[i]);
	}

[Salem]

matrix_augmented already writes it's results into a and v (ie matrix and vector in main).

Which can be passed to gauss as (perhaps - depends how you define gauss)
gauss(r, c, matrix, vector);


How you had things in your previous thread was much better.

[Xavi Camps]

Hello,
I made some changes to my code, now everything seems to work except some of the solutions given by the gauss method. (the first solution x[1] is always wrong). Is it normal that there is no error between multiplying inverse matrix with vector v and the gauss method? (becuase part of my task is to create a graph showing solution vs error).
Here is the new code I am using.

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>


void gauss(int r, int c, double *A[], double B[]);


int main()
{
    srand(time(NULL));
    int r, c, n;
    double Amax = 10, Amin = -10, Bmax = 4, Bmin = -3;
    printf("Enter n :\n");
    scanf("%d", &n);
    printf("\n\n");
    r = n;
    c = n;


    double **A = (double**)malloc(r * sizeof(*A));
    double **Ainv = (double**)malloc(r * sizeof(*Ainv));
    double *B = (double*)malloc(r*sizeof(*B));
    double *X = (double*)malloc(r*sizeof(*X));


    for (int i = 0; i < r; i++)
    {
        A[i] = (double*)malloc(c * sizeof(*A[r]));
    }


    printf("Matrix A:\n");
    for (int i = 0; i < r; ++i)
    {
        for (int j = 0; j < c; ++j)
        {
            A[i][j] = (Amax - Amin) * rand() / RAND_MAX + Amin;
            printf("%lf\t", A[i][j]);
        }
        printf("\n");
    }


    printf("\nMatrix B:\n");
    for (int i = 0; i < r; ++i)
    {
        B[i] = (Bmax - Bmin) * rand() / RAND_MAX + Bmin;
        printf("%lf\n", B[i]);
    }


    double determinant = 0;
    double sum = 0;
    for (int i = 0; i < r; i++)
    {
        Ainv[i] = (double*)malloc(c * sizeof(*Ainv[r]));
    }
    for (int i = 0; i < r; i++)
    {
        determinant = determinant + (A[0][i] * (A[1][(i + 1) % r] * A[2][(i + 2) % r] - A[1][(i + 2) % r] * A[2][(i + 1) % r]));
    }
    printf("\nThe determinanat of A is:    %lf\n", determinant);
    printf("\nInverse of A is: \n\n");
    for (int j = 0; j < r; j++)
    {
        for (int i = 0; i < r; i++)
        {
            Ainv[i][j]=((A[(i + 1) % r][(j + 1) % r] * A[(i + 2) % r][(j + 2) % r]) - (A[(i + 1) % r][(j + 2) % r] * A[(i + 2) % r][(j + 1) % r])) / determinant;
            printf("%lf\t", Ainv[i][j]);
        }
        printf("\n");
    }




    printf("\nResults X: \n");
    for (int i = 0; i < r; i++)
    {
        for (int j = 0; j < r; j++)
        {
            sum = sum + Ainv[j][i] * B[j];
        }
        X[i] = sum;
        printf("X%d=%lf\n", i + 1, X[i]);
        sum = 0;


    }


    gauss(r, c, A, B);
    printf("\n\n");
}




void gauss(int r, int c, double *A[], double B[])
{
    double p, s = 0;
    double **augmented = (double**)malloc(r * sizeof(*augmented));


    for (int i = 0; i < r; i++)
    {
        augmented[i] = (double*)malloc((c+1) * sizeof(*A[r]));
    }


    printf("\naugmented matrix:\n");
    for (int i = 0; i < r; ++i)
    {
        for (int j = 0; j < c; ++j)
        {
            augmented[i][j] = A[i][j];
            printf("%lf\t", augmented[i][j]);


        }
            for (int j = c; j < c + 1; j++)
            {
                augmented[i][j] = B[i];
                printf("%lf\t", augmented[i][j]);
            }


        printf("\n");
    }


    for (int k = 0; k < r - 1; k++)
    {
        for (int i = k + 1; i < r; i++)
        {
            p = augmented[i][k] / augmented[k][k];
            for (int j = k; j < r + 1; j++)
            {
                augmented[i][j] = augmented[i][j] - p*augmented[k][j];
            }
        }
    }


        double *Xgauss = (double*)malloc(r * sizeof(*Xgauss));


        Xgauss[r - 1] = augmented[r - 1][r] / augmented[r - 1][r - 1];
        for (int i = r - 2; i >= 0; i--)
        {
            for (int j = i + 1; j<r; j++)
            {
                s = s + (augmented[i][j] * Xgauss[j]);
                Xgauss[i] = (augmented[i][r] - s) / augmented[i][i];
            }
        }


        printf("\n\nX for gauss method:\n");


        for (int i = 0; i < r; i++)
        {
            printf("X%d=%lf\n", i + 1, Xgauss[i]);
        }
        printf("\n\n");
}