How can I simplify/vectorize this nested loop version of pascals triangle?

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Mark Nelson
Mark Nelson 2018-6-12
评论： OCDER 2018-6-12
%mypascal
n = input('Enter a value for n: ');
% create matrix using nested loops (programming method)
somemat = ones(n);
for i = 2:n
for j = 2:n
somemat(i,j) = somemat(i-1,j) + somemat(i, j-1);
end
end

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OCDER
OCDER 2018-6-12
Behold, a function called pascal
https://www.mathworks.com/help/matlab/ref/pascal.html
S = pascal(n)
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Mark Nelson
Mark Nelson 2018-6-12
@OCDER obviously not what I'm looking for. Perhaps there is no easier way. Thanks anyway.
OCDER
OCDER 2018-6-12
Yeah, I don't think you can vectorize it completely, otherwise Mathwork's pascal would have shown the vectorized code. Since the pascal triangle is symmetric, you could vectorize the filling of the other half of the triangle, which will speed up the code.
For n = 2000, pascal.m is ~ 5 times faster than your pure for loop approach.

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