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Thread: matrix isDiagonaL?
 03282011, 04:10 PM #1Member
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matrix isDiagonaL?
Hi guys im facing with an problem with Matrixes.
Actually what im facing is how to check whether the matrix is diagonal or not
ex: 100
010
001
this is an diagonal matrix.
So my code is like below:
<public boolean isDiagonal() {
int i,j;
for(i=0;i<rows;i++)
{
for(j=0;j<columns;j++)
{
if( (this.checkNull((E) this.vals[i][j]) == false) && (i!=j)){
return false;
}
}
}
return true;
}
private boolean checkNull(E elem){
boolean z = false;
if(( elem.toString().equals("0") )  (elem.toString().equals("false") ))
{
z = true;
}
return z;
}
>
Can u please explain me a bit about this where i did mistake or if anybody know any better solution please show me.
 03282011, 05:19 PM #2Senior Member
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Please use tag for pasting code.
Its hard to understand your code without code tag.
 03282011, 06:54 PM #3Senior Member
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I think below are the indexes you are saying you need to compare. If so you only need one loop. Before I entered the loop I would check that there are an equal number of rows and columns.
foo[0][0]
foo[1][1]
foo[2][2]
foo[3][3]
...
foo[n][n]
 03282011, 08:24 PM #4Member
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public class MatrixDiagonal {
static int[][] matrix = { { 1, 0, 0 }, { 0, 1, 0 }, { 0, 0, 1 }, };
static int positionx = 0, positiony = 0;
static int temp;
static int count = 0;
/**
* @param args
*/
public static void main(String[] args) {
// TODO Autogenerated method stub
for (int i = 0; i <= matrix.length  1; i++) {
for (int j = 0; j <= matrix.length  1; j++) {
temp = matrix[i][j];
if (temp == 1) {
if (positionx == i && positiony == j) {
positionx++;
positiony++;
count++;
}
}
}
}
if (count == matrix.length)
System.out.println(" Matrix have diagonal");
else
System.out.println("matrix dont have");
}
}
try to think it for revers diagonal
001
010
100
or matrix with all primitiv element
 03292011, 03:59 PM #5Member
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So nobody else have any idea about this how can i do better and at least explain it a bit.
 03292011, 04:13 PM #6Senior Member
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1 0 0
0 1 0
0 0 1
what are the indexes of the elements in the diagnol? (I gave you the answer in the earlier post)
How would you loop through this structure to access those elements. (Again a single loop should suffice)
You need to make sure that each diagnol element passes some test ( in this case it looks like it needs to be equal to 1 or they all have to be the same value  I am not sure which one based on your post)
If ANY of the elements fail the test then the method needs to return false
If ALL of the elements pass the test then the method needs to return trueLast edited by yellowledbet; 03292011 at 04:56 PM.
 03292011, 05:00 PM #7Member
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sorry
Sorry I was wrong when i gave the example of isDiagonal matrix:
200
040
001
This is also diagonal matrix its not necessary only 111.
Now i think u got the right question ?
 03292011, 05:24 PM #8Senior Member
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This is still not clear to me.
By your assignment specifications what should the isDiagonal method return for the two structures below?
is this a diagonal (equal values in all diagonal elements)?
200
020
002
is this a diagonal (all diagonal elements are non zero)?
100
020
003
Have you figured out how to write a loop that access the index of each diagonal element?
 03292011, 05:24 PM #9Member
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@bojanm
Sorry man but ur code is not correct to determine either the matrix is diagonal or not for ex:
111
111
111
according to ur code it says is diagonal (in fact this is not diagonal matrix) but i know that ur solution is very well with few mistakes.
to be diagonal need to be like this:
100
030
004
 03292011, 05:26 PM #10Member
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yellowledbet
YEAH both of them are diagonal so how can u make with one loop?? like u said ??
 03292011, 05:30 PM #11Senior Member
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have you tried? what did you come up with
 03292011, 05:34 PM #12Member
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can u please show me how to try by ur idea, really i cant understand ur idea.
 03292011, 05:35 PM #13
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That is incorrect; for a matrix to be diagonal, all the elements at position (i,j) for i != j need to be zero, so you need to check the entire matrix except the elements on the diagonal:
Java Code:for (int i= 0; i < matrix.length; i++) for (int j= 0; j < matrix.length; j++) // assume a square matrix if (i != j && matrix[i][j] != 0) return false; return true;
Joscenosillicaphobia: the fear for an empty beer glass
 03292011, 05:35 PM #14Member
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I think the only way is using nested loop
 03292011, 05:36 PM #15Member
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So this is two for loop not one lol.
 03292011, 05:37 PM #16Member
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Isnt same code like i posted first post????
 03292011, 05:38 PM #17
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 03292011, 05:40 PM #18Member
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Thank u :D for ur solution I really appreciate it.
 03292011, 05:44 PM #19Senior Member
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Is one loop really incorrect?
 03292011, 05:47 PM #20
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Yep, if any of the numbers not on the main diagonal is nonzero the matrix is not a diagonal matrix; you have to check all those elements in each row and each column. Without trickerydickery you need two loops, one for the rows and one for the columns of the matrix.
kind regards,
Joscenosillicaphobia: the fear for an empty beer glass
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