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Topic: doing transforms and inverses on a matrix (Read 996 times) |
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sspboyd
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doing transforms and inverses on a matrix
« on: May 24th, 2004, 10:59pm » |
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Hello,
I am trying to figure out how to 'rotate' or 'flip' a 5X3 matrix.
Does anyone have an example they could share or point me towards some helpful urls?
Thanks,
steve
eg
Code:
1| 2| 3| 4| 5
____________
6| 7| 8| 9|10
____________
11|12|13|14|15
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rotate to
Code:
11| 6| 1
--------
12| 7| 2
--------
13| 8| 3
--------
14| 9| 4
--------
15|10| 5
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thanks
steve
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gmail.com w/ sspboyd username
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TomC
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Re: doing transforms and inverses on a matrix
« Reply #2 on: May 24th, 2004, 11:32pm » |
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I think it's maths Mikkel 
Answer... depends how they're stored.
Naively, given:
Code:
int matrix[] = {
1, 2, 3, 4, 5,
6, 7, 8, 9, 10,
11, 12, 13, 14, 15
};
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The rotated version you request is...
Code:
int rotated[] = {
matrix[10], matrix[5], matrix[0],
matrix[11], matrix[6], matrix[1],
matrix[12], matrix[7], matrix[2],
matrix[13], matrix[8], matrix[3],
matrix[14], matrix[9], matrix[4]
};
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Which you can use like this...
Code:
int matrix[] = {
1, 2, 3, 4, 5,
6, 7, 8, 9, 10,
11, 12, 13, 14, 15
};
void setup() {
println("matrix:");
for (int i = 0; i < matrix.length; i+=5) {
println(matrix[i] + ", " + matrix[i+1] + ", " + matrix[i+2] + ", " + matrix[i+3] + ", " + matrix[i+4]);
}
int rotated[] = {
matrix[10], matrix[5], matrix[0],
matrix[11], matrix[6], matrix[1],
matrix[12], matrix[7], matrix[2],
matrix[13], matrix[8], matrix[3],
matrix[14], matrix[9], matrix[4]
};
println("rotated:");
for (int i = 0; i < rotated.length; i+=3) {
println(rotated[i] + ", " + rotated[i+1] + ", " + rotated[i+2]);
}
}
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sspboyd
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Re: doing transforms and inverses on a matrix
« Reply #4 on: May 25th, 2004, 12:58am » |
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excellent. thanks (again) tom. Is there a way to do this algorithmically so that I can use random sizes of matrices? Or would this require using Jama?
http://math.nist.gov/javanumerics/jama/
I was getting to the point of considering outputting an image of grey rects where the float vals in the matrix corresponded to the grey level, then flip/rotating or whatever the image and reading out the colour vals again into a new matrix.
I am also thinking about using a modified version of mKoser's suggestion too.
Thanks for the quick response.
steve
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gmail.com w/ sspboyd username
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TomC
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Re: doing transforms and inverses on a matrix
« Reply #5 on: May 25th, 2004, 1:16am » |
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I think if you have a 2D array of this form:
Code:
int matrix[][] = {
{ 1, 2, 3, 4, 5 },
{ 6, 7, 8, 9, 10 },
{ 11, 12, 13, 14, 15 }
};
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Then this is a general function that will flip it like you want:
Code:
int[][] rotateMatrix(int[][]given) {
int rotated[][] = new int[given[0].length][given.length];
for (int i = 0; i < given[0].length; i++) {
for (int j = 0; j < given.length; j++) {
rotated[i][j] = given[given.length-1-j][i];
}
}
return rotated;
}
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It assumes there is at least one row, and that all rows are the same length.
You could write similar code to do a 1D array, if you know the width and height.
If you're doing it to pixels (images), it's probably more flexible to use transforms (translate, rotate, scale, etc).
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| « Last Edit: May 25th, 2004, 1:18am by TomC » |
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sspboyd
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Re: doing transforms and inverses on a matrix
« Reply #6 on: May 25th, 2004, 10:23am » |
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Quote:
If you're doing it to pixels (images), it's probably more flexible to use transforms (translate, rotate, scale, etc).
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Im actually doing it to a probability matrix that does eventually end up as pixels but I don't want to copy the pixels from the results of one matrix and use them again (or else it wouldn't be a probability matrix).
Thanks for your help. I will let you know how the program turns out when I get time to finish it.
steve
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gmail.com w/ sspboyd username
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