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Feb 13th, 2005

Transpose a matrix

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I need help with transposing a matrix.

I already did the transpose matrix using 2 arrays.

But I can't figure out how to do it using only one array.
So read a matrix and create the transpose within itself.
Do I use the swap or what?

Any help would be great.

Later

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mariners95

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Feb 13th, 2005

Re: Transpose a matrix

If it's a square matrix then you can do it with something like this:

C Syntax (Toggle Plain Text)
for (int i = 0; i < 4; i++) {
  for (int j = i + 1; j < 4; j++) {
    int save = matrix[i][j];
    matrix[i][j] = matrix[j][i];
    matrix[j][i] = save;
  }
}
for (int i = 0; i < 4; i++) {
  for (int j = i + 1; j < 4; j++) {
    int save = matrix[i][j];
    matrix[i][j] = matrix[j][i];
    matrix[j][i] = save;
  }
}

If it's a non-square matrix then you're SOL.

Narue

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Feb 15th, 2005

Re: Transpose a matrix

Quote originally posted by Narue ...

If it's a square matrix then you can do it with something like this:
C Syntax (Toggle Plain Text)
for (int i = 0; i < 4; i++) {
  for (int j = i + 1; j < 4; j++) {
    int save = matrix[i][j];
    matrix[i][j] = matrix[j][i];
    matrix[j][i] = save;
  }
}
for (int i = 0; i < 4; i++) { for (int j = i + 1; j < 4; j++) { int save = matrix[i][j]; matrix[i][j] = matrix[j][i]; matrix[j][i] = save; } }
If it's a non-square matrix then you're SOL.

Your program won't work. The reason is that when you write matrix[i][j] = matrix[j][i] you've lost the contents of matrix[i][j] forever and you can't get it back to put in position [[j][i]. This will do it.

C Syntax (Toggle Plain Text)
for (int i = 0; i < 4; i++)
   for (int j = 0; j < 4; j++)
    {   save = matrix[i][j];
        matrix[i][j] = matrix[j][i];
         matrix[j][i] = save;
    }
for (int i = 0; i < 4; i++)
   for (int j = 0; j < 4; j++)
    {   save = matrix[i][j];
        matrix[i][j] = matrix[j][i];
         matrix[j][i] = save;
    }

murschech

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Feb 15th, 2005

Re: Transpose a matrix

Quote originally posted by Narue ...

If it's a square matrix then you can do it with something like this:
C Syntax (Toggle Plain Text)
for (int i = 0; i < 4; i++) {
  for (int j = i + 1; j < 4; j++) {
    int save = matrix[i][j];
    matrix[i][j] = matrix[j][i];
    matrix[j][i] = save;
  }
}
for (int i = 0; i < 4; i++) { for (int j = i + 1; j < 4; j++) { int save = matrix[i][j]; matrix[i][j] = matrix[j][i]; matrix[j][i] = save; } }
If it's a non-square matrix then you're SOL.

Sorry. I didn't read your code carfully enough before I replied.

murschech

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Feb 15th, 2005

Re: Transpose a matrix

>Sorry. I didn't read your code carfully enough before I replied.
Maybe you should run example code to see if it works before trying to correct it with an incorrect solution. Starting the inner loop at 0 instead of i + 1 will result in a lot of shuffling to get the same matrix that you started with, not a transposed matrix as the OP requested. So maybe you should also test your own code before posting it. Especially if you're trying to correct someone and using it as an example.

On a purely stylistic point, I have two issues with your code. First, even though it's valid the way you did it, you should always put braces around a loop or if construct that has more than a one line body. This way you don't have to rely solely on indention to prove that your code is correct. You also avoid certain pitfalls.

Second, starting the statements of a block on the same line as the opening brace is a formatting nightmare. It makes code harder to read and harder to reformat so that it's easier to follow.

Something more like this (following your apparent brace indention style):

C Syntax (Toggle Plain Text)
for (int i = 0; i < 4; i++)
 {
   for (int j = 0; j < 4; j++)
    {
       save = matrix[i][j];
       matrix[i][j] = matrix[j][i];
       matrix[j][i] = save;
    }
 }
for (int i = 0; i < 4; i++)
 {
   for (int j = 0; j < 4; j++)
    {
       save = matrix[i][j];
       matrix[i][j] = matrix[j][i];
       matrix[j][i] = save;
    }
 }

You also failed to define save before using it, but I'll let you slide on that.

Narue

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Sep 30th, 2007

Re: Transpose a matrix

How to make a program yhat make the transpose of a matrix using array and pointers C ofcourse?

aldrinsms

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Sep 30th, 2007

Re: Transpose a matrix

Wonderful! Be a pompous ass and dredge up an old thread (after reiterating the same demand a 3rd time), offering nothing, and pretend you are being courteous! Well, done. *plonk*

Dave Sinkula

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Nov 23rd, 2008

Re: Transpose a matrix

// prog to mulltiply matrix

c Syntax (Toggle Plain Text)
#include<stdio.h>
#include<conio.h>
void main()
{
int a[10][10],b[10][10],c[10][10],i,j,k,m,n,m1,n1;
clrscr();
printf("Enter array size ");
scanf("%d%d",&m,&n);
printf("Enter array size 2");
scanf("%d%d",&m1,&n1);
if(n!=m1)
{
printf("Wrong choice entered");
getch();
exit(0);
}
else
{
printf("Enter elements");
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
scanf("%d",&a[i][j]);
}
}
printf("Enter element 2");
for(i=0;i<m1;i++)
{
for(j=0;j<n1;j++)
{
scanf("%d",&b[i][j]);
}
}
for(i=0;i<m;i++)
{
for(j=0;j<n1;j++)
{
c[i][j]=0;
for(k=0;k<n;k++)
{
c[i][j]=c[i][j]+(a[i][k]*b[k][j]);
}
}
}
printf("REQUIRED MATRIX");
for(i=0;i<m;i++)
{
for(j=0;j<n1;j++)
{
printf("\n%d",c[i][j]);
}
printf("\n");
}
getch();
}
}
#include<stdio.h>
#include<conio.h>
void main()
{
int a[10][10],b[10][10],c[10][10],i,j,k,m,n,m1,n1;
clrscr();
printf("Enter array size ");
scanf("%d%d",&m,&n);
printf("Enter array size 2");
scanf("%d%d",&m1,&n1);
if(n!=m1)
{
printf("Wrong choice entered");
getch();
exit(0);
}
else
{
printf("Enter elements");
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
scanf("%d",&a[i][j]);
}
}
printf("Enter element 2");
for(i=0;i<m1;i++)
{
for(j=0;j<n1;j++)
{
scanf("%d",&b[i][j]);
}
}
for(i=0;i<m;i++)
{
for(j=0;j<n1;j++)
{
c[i][j]=0;
for(k=0;k<n;k++)
{
c[i][j]=c[i][j]+(a[i][k]*b[k][j]);
}
}
}
printf("REQUIRED MATRIX");
for(i=0;i<m;i++)
{
for(j=0;j<n1;j++)
{
printf("\n%d",c[i][j]);
}
printf("\n");
}
getch();
}
}

Last edited by Ancient Dragon; Mar 23rd, 2009 at 3:53 pm. Reason: add code tags

MANDALSHASHI

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Mar 23rd, 2009

Re: Transpose a matrix

Hi there
I read you method of transposing a matrix
it works
but i have toa sk a question!
that what is the logic behind initializing inner loop variable j=i+1 instead of j=0???
i shalll be thankful to you if you reply to this post
thanx

thinkammar

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Mar 23rd, 2009

Re: Transpose a matrix

>>what is the logic behind initializing inner loop variable j=i+1 instead of j=0???

which post # are you talking about?

Ancient Dragon

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