Thread: Need a real help please!!

Hi, I'm applying and doing a code that's printing the upper-trinqular of the given matrix, I've successfully done the code for printing what I demanded, but there's one specific error that I need a real help in it which is whenever I enter a matrix initialized with value 0, (matrix[0][0]=0) my code prints wrong result and something unclear for me at all and it's just when I enter the first matrix's value as 0.


here's my code:

Code:

#include<stdio.h>
#include<conio.h>


float matrix[10][10], m;
int i, j, k, n;
void upper_triangularization() {
	for (i = 0; i<n - 1; i++)
		for (j = i + 1; j<n; j++) {
			m = matrix[j][i] / matrix[i][i];
			for (k = 0; k<n + 1; k++) {
				matrix[j][k] = matrix[j][k] - (m*matrix[i][k]);
			}
		}
} //upper_traingulisation
void main() {
	printf("Enter number. of column :: ");
	scanf("%d", &n);
	printf("Enter the augmented matrix: \n");
	for (i = 0; i<n; i++)
		for (j = 0; j<n ; j++)
			scanf("%f", &matrix[i][j]);


	upper_triangularization();


	printf("The upper traingular matrix is : \n");


	for (i = 0; i<n; i++) {
		for (j = 0; j<n; j++)
			printf("%f \t", matrix[i][j]);
		printf("\n");
	}
}

Any help please?

thanks in advance!!

Originally Posted by laserlight

Grr... use local variables, not global variables! What exactly is your test input, expected output, and actual output?

I tested matrix
0 1
1 0


I tried ur suggestion about local and global...the same results.
My problem occurred whenever I enter the first value as 0.

Yes laser;
I know it's prevented to divide on Zero..but not benefit because I got the same result..wrong printf

Laser I'm sorry about that...I didn't understand you very well...sorry about that.
My program in brief is converting the given matrix to a upper-triangular matrix...
And regarding to my problem is just occurring whenever I enter the value 0 in the first value of the given matrix

Originally Posted by laserlight

That's too bad. I might have a chance at helping you debug if you described what the program is supposed to do and told me what exactly is your test input, expected output, and actual output, but since you refuse to so, I guess I'll have to give up. Thankfully, it is not my program, so I do not have to be bothered.

My test input is double numbers...
I have tested
0
1
1
0
And got the problem

Originally Posted by RyanC

My test input is double numbers...
I have tested
0
1
1
0
And got the problem

Again, this is like 1/3 of the question asked. To clarify what we want you to answer... imagine a perfect world. When you enter this information, what is supposed to come out? And when you answer that, what actually comes out? You know it's polite to have a reference, so we know we're doing the right thing, instead of you just depending on us to run your example and come up with the right answer.

The question is in abbreviation "You must find the upper-triangular of the given matrix by algebraically way and print the uppers triangular on the screen"

What I have done is working fine as expected unless one thing which is whenever I put the first value of the given matrix 0..the code starts printing weird things.

Originally Posted by RyanC

Yes laser;
I know it's prevented to divide on Zero..but not benefit because I got the same result..wrong printf

Well, your code failed a simple assertion:

Code:

#include <assert.h>

void upper_triangularization() {
    for (i = 0; i<n - 1; i++)
        for (j = i + 1; j<n; j++) {
            assert(matrix[i][i] != 0.0 && "division by zero detected!");
            m = matrix[j][i] / matrix[i][i];
            for (k = 0; k<n + 1; k++) {
                matrix[j][k] = matrix[j][k] - (m*matrix[i][k]);
            }
        }
} //upper_traingulisation


sh-4.3$ main                                                                                                                                                            

Enter number. of column :: 2                                                                                                                                            

Enter the augmented matrix:                                                                                                                                             

0 1                                                                                                                                                                     

1 0                                                                                                                                                                     

main: main.c:9: upper_triangularization: Assertion `matrix[i][i] != 0.0 && "division by zero detected!"' failed.

So even though you say it's prevented, it clearly is not. This would explain the -nans and -infs you get as output.

What I resent is that you would not provide sample outputs yourself! How hard is it, really?!?

Originally Posted by whiteflags

Well, your code failed a simple assertion:

Code:

#include <assert.h>

void upper_triangularization() {
    for (i = 0; i<n - 1; i++)
        for (j = i + 1; j<n; j++) {
            assert(matrix[i][i] != 0.0 && "division by zero detected!");
            m = matrix[j][i] / matrix[i][i];
            for (k = 0; k<n + 1; k++) {
                matrix[j][k] = matrix[j][k] - (m*matrix[i][k]);
            }
        }
} //upper_traingulisation


sh-4.3$ main                                                                                                                                                            

Enter number. of column :: 2                                                                                                                                            

Enter the augmented matrix:                                                                                                                                             

0 1                                                                                                                                                                     

1 0                                                                                                                                                                     

main: main.c:9: upper_triangularization: Assertion `matrix[i][i] != 0.0 && "division by zero detected!"' failed.

So even though you say it's prevented, it clearly is not. This would explain the -nans and -infs you get as output.

What I resent is that you would not provide sample outputs yourself! How hard is it, really?!?

I avoided that thing in my code after edition (didn't post it) but whatever it's still printing wrong printf ( I added a new condition for the possibility of 0, whenever there's 0 then divide conversely (0/a=0)

I really in need of help, any clue?

In what way is it printing wrong? I am not a mind reader.