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From: Guangping Zhang on 28 Jan 2010 23:38
Dear All,

I'm a new Matlab people and need your help.
I do have multiple variables, A1, A2, A3... in one .mat file for analysis. The matrix A1,A2,A3 have same size. I have another B1,B2,B3...I will do this:

A1-B1,A2-B2,A3-B3,...

and analyze all of them. How can I write a for loop to do it? I write one, but it never work,
like this:
for i=1:30
Ci=Ai+Bi
end

I know Ai is a string, but I don't know how to use eval function to do it.

I will appreciate any help.

zgp480
From: kinor on 29 Jan 2010 02:55
"Guangping Zhang" <zgp480(a)gmail.com> wrote in message <hjtonc$l7a$1(a)fred.mathworks.com>...
> Dear All,
>
> I'm a new Matlab people and need your help.
> I do have multiple variables, A1, A2, A3... in one .mat file for analysis. The matrix A1,A2,A3 have same size. I have another B1,B2,B3...I will do this:
>
> A1-B1,A2-B2,A3-B3,...
>
> and analyze all of them. How can I write a for loop to do it? I write one, but it never work,
> like this:
> for i=1:30
> Ci=Ai+Bi
> end
>
> I know Ai is a string, but I don't know how to use eval function to do it.
>
> I will appreciate any help.
>
> zgp480

help eval
From: us on 29 Jan 2010 03:36
"Guangping Zhang" <zgp480(a)gmail.com> wrote in message <hjtonc$l7a$1(a)fred.mathworks.com>...
> Dear All,
>
> I'm a new Matlab people and need your help.
> I do have multiple variables, A1, A2, A3... in one .mat file for analysis. The matrix A1,A2,A3 have same size. I have another B1,B2,B3...I will do this:
>
> A1-B1,A2-B2,A3-B3,...
>
> and analyze all of them. How can I write a for loop to do it? I write one, but it never work,
> like this:
> for i=1:30
> Ci=Ai+Bi
> end
>
> I know Ai is a string, but I don't know how to use eval function to do it.
>
> I will appreciate any help.
>
> zgp480

one of the solutions
- do NOT do it this way

% the data
% - create a MAT-file (should never do it this way...)...
fnam='foo.mat'; % <- your file name
a1=1:2;
a2=3:4;
a3=5:6;
save(fnam,'a1','a2','a3');
clear a*;
% the engine
m=load(fnam);
m=struct2cell(m);
m=cat(1,m{:}); % <- since your data has the same size...
disp(m);
%{
1 2 % <- a1
3 4 % <- a2
5 6 % <- ...
%}
% - now, use indexing, which is especially helpful for a loop construct, eg,
r=m(1,:)-m(2,:) % <- a1-a2
% r = -2 -2

us
From: Sebastian Hölz on 29 Jan 2010 03:59
Easy way without eval:

% 'file.mat'contains A1, B1, ..., An, Bn, and is loaded into structure
dat = load('file.mat');

% Now iterate over all fields Ai and Bi
n = length(fieldnames(dat))/2;
for i=1:n
dat.(sprintf('C%i',i)) = dat.(sprintf('A%i',i))+dat.(sprintf('B%i',i));
% This is dat.Ci = dat.Ai+dat.Bi, see help for structs
end

Sebastian
From: Guangping Zhang on 30 Jan 2010 13:00
I really appreciate the help from all the response. the solution works so good.


Yours,
Guangping,

"Sebastian Hölz" <seppel_mit_pp(a)web.de> wrote in message <hju80o$6i8$1(a)fred.mathworks.com>...
> Easy way without eval:
>
> % 'file.mat'contains A1, B1, ..., An, Bn, and is loaded into structure
> dat = load('file.mat');
>
> % Now iterate over all fields Ai and Bi
> n = length(fieldnames(dat))/2;
> for i=1:n
> dat.(sprintf('C%i',i)) = dat.(sprintf('A%i',i))+dat.(sprintf('B%i',i));
> % This is dat.Ci = dat.Ai+dat.Bi, see help for structs
> end
>
> Sebastian
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