Variable name dynamically changing [really noob]
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From: Andy on 15 Jul 2010 09:03 > Problem here is that YtransMatrix_i are really 4 2x2 matrices full of data. The names YtransMatrix_0 to YtransMatrix_3 come from 4 devices named from 0 to 3. > Then I want to construct another matrix Mx whose elements are functions of the elements of the YtransMatrix [in the example I showed you the first column but it will be 4x3 matrix with also coupled elements of different YtransMatrix] If you have 4 matrices each 2x2, then the correct way to store them is in a 2x2x4 array, YtransMatrix. Then YtransMatrix(:,:,1) would be what you now call YtransMatrix_0; YtransMatrix(:,:,2) would be what you now call YtransMatrix_1; etc. You can then solve your original problem as follows: YtransMatrix = reshape(1:16,[2 2 4]); % some sample data %{ % the matrix displayed YtransMatrix(:,:,1) = 1 3 2 4 YtransMatrix(:,:,2) = 5 7 6 8 YtransMatrix(:,:,3) = 9 11 10 12 YtransMatrix(:,:,4) = 13 15 14 16 % your desired output would be the (1,1) element of each of these slices squared % hence [1 25 81 169] %} Mx(1:4) = squeeze(YtransMatrix(1,1,:).^2); % see help squeeze for more on squeeze
From: Javier on 15 Jul 2010 09:25 "Andy " <myfakeemailaddress(a)gmail.com> wrote in message <i1n0ue$hj4$1(a)fred.mathworks.com>... > > Problem here is that YtransMatrix_i are really 4 2x2 matrices full of data. The names YtransMatrix_0 to YtransMatrix_3 come from 4 devices named from 0 to 3. > > Then I want to construct another matrix Mx whose elements are functions of the elements of the YtransMatrix [in the example I showed you the first column but it will be 4x3 matrix with also coupled elements of different YtransMatrix] > > If you have 4 matrices each 2x2, then the correct way to store them is in a 2x2x4 array, YtransMatrix. Then YtransMatrix(:,:,1) would be what you now call YtransMatrix_0; YtransMatrix(:,:,2) would be what you now call YtransMatrix_1; etc. You can then solve your original problem as follows: > > > YtransMatrix = reshape(1:16,[2 2 4]); % some sample data > > %{ > % the matrix displayed > YtransMatrix(:,:,1) = > > 1 3 > 2 4 > > YtransMatrix(:,:,2) = > > 5 7 > 6 8 > > YtransMatrix(:,:,3) = > > 9 11 > 10 12 > > YtransMatrix(:,:,4) = > > 13 15 > 14 16 > > % your desired output would be the (1,1) element of each of these slices squared > % hence [1 25 81 169] > %} > > Mx(1:4) = squeeze(YtransMatrix(1,1,:).^2); > > % see help squeeze for more on squeeze Thank you very much! Now it's clear :)
From: Steven Lord on 15 Jul 2010 09:40 "Javier " <jagon(a)postal.uv.es> wrote in message news:i1mltp$a1v$1(a)fred.mathworks.com... > Hi guys, > a real basic question I guess. But I didn't had a course on that and I'm > learning on my own. > > I have four matrices, whose (1,1) elements are, say: > > YtransMatrix_0(1,1) = 0; > YtransMatrix_1(1,1) = 1; > YtransMatrix_2(1,1) = 2; > YtransMatrix_3(1,1) = 3; > > I want to create one matrix with the first column being the elements > before to the second power. I would like to do it in a quick form taking > advantage of the index in the name of the four matrices YtransMatrix_i > > I tried something like: > > Mx(1:4,1)=pow(sprintf('YtransMatrix_%d(1,1)',0:3),2); > > But that's not working. I don't know how to manage an index in the > variable name. Others have given alternate approaches (a 3-D array being one; a cell array would be another.) If you're curious why people are so insistent that you move away from this type of naming scheme, take a look at question 4.6 in the newsgroup FAQ (linked in my signature.) -- Steve Lord slord(a)mathworks.com comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ To contact Technical Support use the Contact Us link on http://www.mathworks.com
From: Javier on 15 Jul 2010 11:10 "Steven Lord" <slord(a)mathworks.com> wrote in message <i1n33v$8es$1(a)fred.mathworks.com>... > > "Javier " <jagon(a)postal.uv.es> wrote in message > news:i1mltp$a1v$1(a)fred.mathworks.com... > > Hi guys, > > a real basic question I guess. But I didn't had a course on that and I'm > > learning on my own. > > > > I have four matrices, whose (1,1) elements are, say: > > > > YtransMatrix_0(1,1) = 0; > > YtransMatrix_1(1,1) = 1; > > YtransMatrix_2(1,1) = 2; > > YtransMatrix_3(1,1) = 3; > > > > I want to create one matrix with the first column being the elements > > before to the second power. I would like to do it in a quick form taking > > advantage of the index in the name of the four matrices YtransMatrix_i > > > > I tried something like: > > > > Mx(1:4,1)=pow(sprintf('YtransMatrix_%d(1,1)',0:3),2); > > > > But that's not working. I don't know how to manage an index in the > > variable name. > > Others have given alternate approaches (a 3-D array being one; a cell array > would be another.) If you're curious why people are so insistent that you > move away from this type of naming scheme, take a look at question 4.6 in > the newsgroup FAQ (linked in my signature.) > > -- > Steve Lord > slord(a)mathworks.com > comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ > To contact Technical Support use the Contact Us link on > http://www.mathworks.com > Thak you very much. I'll give a look at this. Just another thing about preallocating. I made it like this because I had a warning saying that preallocating would be faster than a for loop: My(1:4,3)=pow(YtransfMatrix(1,2,1:4),2); and it should work. But, how to make this when I have something like: For i=1:4 Mxy(i,2)=XtransfMatrix(1,1,i)*YtransfMatrix(1,2,i); end He says to me that I should preallocate for speed. But I cannot make in the way like before: Mxy(1:4,2)=XtransfMatrix(1,1,1:4)*YtransfMatrix(1,2,1:4); Obviously second part of equation is 4 by 4, not 4 by 1.
From: Andy on 15 Jul 2010 11:45 Since you appear to want to multiply element by element, you should use the .* operator instead of just the * operator.
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