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If I start with a matrix of zeros, how can I easily create a triangle of ones in that matrix?

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Daniel Gray
Daniel Gray 2017-6-19
评论： Image Analyst 2017-6-21
I want to be able to get a .mat file that will create a filled triangle when I use imagesc. I have been told the easiest way is to start with a matrix full of zeros and then create a triangle of ones inside of that, but I can not figure out how to do that, other than manually which would take a while.

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KSSV
KSSV 2017-6-19
N = 100 ;
T1 = triu(ones(N),1) ;
T2 = fliplr(T1) ;
T = [T2 T1] ;
figure(1)
imagesc(T)

更多回答（3 个）

Andrei Bobrov
Andrei Bobrov 2017-6-19
N = 1000;
T = tril(ones(N)) ;
a = round(imresize([flip(T,2),T],[round(N/2*tan(pi/3)) N]));
imagesc(a)
Image Analyst
Image Analyst 2017-6-19
If you have the Image Processing Toolbox, it's a simple one liner:
triangleMatrix = poly2mask(x, y, rows, columns);
where x and y are 3 element arrays of the rows and columns where you want the vertices, and rows and columns are the overall size of your output matrix. Be careful not to mix up x and y with row and column - remember (x,y) = (column,row), not (row, column).
Adam
Adam 2017-6-19
It depends where you want the triangle. For example
res = tril( ones(100) );
will produce a triangle in the lower left of the matrix.
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