# creating an equal lateral triangle in matrix

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Nathan Sulzer 2018 年 11 月 10 日
コメント済み: John D'Errico 2018 年 11 月 10 日
Is there an easy method for generating an equal lateral triangle centered and the middle of a matrix? The image attached is what I want the matrix to look like except the triangle would be made of 1s and the background zero. Thank you in advanced.

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### 回答 (2 件)

jonas 2018 年 11 月 10 日

You could do something like this:
poly = polyshape([1 2 1.5],[1 1 2])
plot(poly)
set(gca,'xcolor','none','ycolor','none')
F = getframe(gca)
I = imbinarize(rgb2gray(F.cdata))
imshow(~I)
change coordinates of the polygon to create your desired triangle.
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John D'Errico 2018 年 11 月 10 日
Drat. Polyshape has not been around long enough that I think of it immediately. :)

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John D'Errico 2018 年 11 月 10 日
Any number of ways, certainly many if I spent any amount of time to think them up. Simplest?
1. Start with meshgrid, creating sets of indices into the final array.
2. Create a polygon, that denotes the corners of the triangle.
3. Use inpolygon to indicate which points lie inside the triangle.
4. Assign the array initially uing zeros.
5. Use logical indexing to overwrite the points inside the polygon as 1.
So simple and fast, fully vectorized. But many other ways too.

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