Creating a matrix without using for loop

Question

I want to generate a n*n matrix in MATLAB, where each entry is A(i,j) = j^i, i=j=1...n but without using a for loop. In the MATLAB help, I saw a function matrix(m,n,f), but I don't know how to use that one.

Please provide a sample output to make clear what you are after. What is i=j=n in your equation? — nispio
– nispio, Commented Oct 30, 2013 at 23:02

Luis Mendo · Accepted Answer · 2013-10-30 23:13:39Z

4

You can do it easily with bsxfun:

A = bsxfun(@power, 1:n, (1:n).');

answered Oct 30, 2013 at 23:13

Luis Mendo

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3 Comments

Joey Over a year ago

Thanks!by the way, what's the meaning of (1:n).' ？

chappjc Over a year ago

@Joey Cheng - See help punct for an interesting description of the punctuation operators in MATLAB. This is the non-conjugate transpose.

Luis Mendo Over a year ago

@JoeyCheng It is a column vector from 1 to n. You should read help punct as @chappjc says, it is very useful

David · Accepted Answer · 2013-10-30 23:09:28Z

2

Is this what you are after?

[A,b]=meshgrid(1:n);
M=A.^b;

edited Oct 30, 2013 at 23:09

answered Oct 30, 2013 at 22:59

David

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5 Comments

Joey Over a year ago

not exactly, I want every entry Aij to be j^i, so if n = 3, I will get [1,2,3;1,4,9;1,8,27], and can you explain the mechanisms behind the equation, by which I mean the meaning of the (1:n) the ' and the * means? Thanks a lot!

nispio Over a year ago

@JoeyCheng Please edit your question to include this information, instead of placing it in the comments. You can do this by clicking the "edit" button under your post.

David Over a year ago

@nispio I think his question is alright (apart from the i=j=n part). I had initially misread it as each element being i*j not i^j. It was my mistake.

Joey Over a year ago

Thanks so much David, but can you briefly explain what is the meaning of meshgrid(1:n) and A.^b?

David Over a year ago

Sure. Meshgrid link takes two vectors and constructs two matrices which give all the combinations of the input vectors. In this case, the input vector is 1:n which is the vector [1 2 3 4 5 ... n]. So you get two matrices like [1 1 1;2 2 2;3 3 3] and [1 2 3;1 2 3;1 2 3]. Then the A.^b is taking each element of A and raising it to the power of the corresponding element in b link. Hope that helps.

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