how to switch from C language to matlab?

i should rewrite this code in C on matlab

#include<stdio.h>
int main()
{
    int i,j,k,n;
    float A[20][20],c,x[10],sum=0.0;
    printf("\nEnter the order of matrix: ");
    scanf("%d",&n);
    printf("\nEnter the elements of augmented matrix row-wise:\n\n");
    for(i=1; i<=n; i++)
    {
        for(j=1; j<=(n+1); j++)
        {
            printf("A[%d][%d] : ", i,j);
            scanf("%f",&A[i][j]);
            }
        }
        for(j=1; j<=n; j++) /* loop for the generation of upper triangular matrix*/
        {
            for(i=1; i<=n; i++)
            {
                if(i>j)
                {
                    c=A[i][j]/A[j][j];
                    for(k=1; k<=n+1; k++)
                    {
                        A[i][k]=A[i][k]-c*A[j][k];
                    }
                }
            }
        }
        x[n]=A[n][n+1]/A[n][n];
        /* this loop is for backward substitution*/
        for(i=n-1; i>=1; i--)
        {
            sum=0;
            for(j=i+1; j<=n; j++)
            {
                sum=sum+A[i][j]*x[j];
            }
            x[i]=(A[i][n+1]-sum)/A[i][i];
        }
        printf("\nThe solution is: \n");
        for(i=1; i<=n; i++)
        {
            printf("\nx%d=%f\t",i,x[i]); /* x1, x2, x3 are the required solutions*/
        }
        return(0);
    }

[Geoff Hayes]

@AURORA SCALINCI - what have you tried so far? Please see scripts vs functions, matrices and arrays and for to get an idea of where to start.

Answer 1

[Pratik Pawar]

This code is performing Gaussian Elimination.

Please refer to the C code converted to MATLAB below:

% script_name.m

% input augmented matrix

n = input('Enter the order of matrix: ');

disp(' ');

A = zeros(n, n+1);

for i=1:n

for j=1:n+1

A(i,j)=input(sprintf('Input the matrix value for (%d,%d): ', i, j));

end

end

% separate last column of augmented matrix as b and define x

b = A(1:n, n+1);

% forward elimination code to convert matrix A to upper triangular matrix

for j = 1:n-1

for i = n:-1:j+1

m = A(i,j)/A(j,j);

A(i,:) = A(i,:) - m*A(j,:);

b(i) = b(i) - m*b(j);

end

end

% back substitution to find x

x = zeros(n,1);

x(n) = b(n)/A(n,n);

for i = n-1:-1:1

sum = 0;

for j = n:-1:i+1

sum = sum + A(i,j)*x(j);

end

x(i) = (b(i)- sum)/A(i,i);

end

% display roots

x

MATLAB allows processing all the values in a matrix using single arithmatic operator. So, a doble 'for loop' can be avoided to improve time complexity.

% preferred

% script_name.m

% input augmented matrix

n = input('Enter the order of matrix: ');

disp(' ');

A = zeros(n, n+1);

for i=1:n

for j=1:n+1

A(i,j)=input(sprintf('Input the matrix value for (%d,%d): ', i, j));

end

end

% separate last column of augmented matrix as b and define x

b = A(1:n, n+1);

x = zeros(n, 1);

% forward elimination code to convert matrix A to upper triangular matrix

for i=1:n-1

m = A(i+1:n, i) / A(i, i);

A(i+1:n, :) = A(i+1:n, :) - m*A(i, :);

b(i+1:n, :) = b(i+1:n, :) - m*b(i, :);

end

% back substitution to find x

x(n, :) = b(n, :) / A(n, n);

for i=n-1:-1:1

x(i, :) = (b(i, :) - A(i, i+1:n)*x(i+1:n, :))/A(i, i);

end

% display roots

x