Comments on: MATLAB Basics video: Storing data in a matrix from a loop

By: dhull

dhull — Mon, 22 Nov 2010 16:59:48 +0000

@Santiago

m(loopNumber,:) = vec

By: santiago vacca

santiago vacca — Mon, 22 Nov 2010 16:58:30 +0000

Dear Doug,

I have a loop and i create a vector form each run, i want to store those vectors (in a matrix wold be fine). What´s the easy way?

Thanks very much,
Santiago.

By: dhull

dhull — Fri, 24 Sep 2010 20:33:50 +0000

a = [1 2 3]
b = [4 5 6]
c = [7 8 9]
M(1,:) = a
M(2,:) = b
M(3,:) = c

By: Tachibana49

Tachibana49 — Thu, 23 Sep 2010 08:23:45 +0000

Thanks for your tutorial, Doug.
But my problem is how to store polynomial roots into a matrix.
I got an open channel flow problem and came out with a cubic function with different coefficients at various conditions.
I tried to use loop to get the roots for all conditions and wanted to extract all roots. I used index, but MATLAB requires “In an assignment A(I) = B, the number of elements in B and I must be the same.”

So how can I store all 3 roots of each polynomial function into a matrix?
I will really appreciate your help.

By: dhull

dhull — Tue, 16 Feb 2010 19:47:53 +0000

>> m = magic(3)


m =

     8     1     6
     3     5     7
     4     9     2

>> r = find((m(:,1) == 8) & (m(:,2) < 3))

r =

     1

By: vinay bansal

vinay bansal — Tue, 16 Feb 2010 17:38:36 +0000

sir, but my problem is related to “find” …i want to find some value in first column and also some other value in second column…..n then i want that row where the both value exist.

By: dhull

dhull — Tue, 16 Feb 2010 17:09:16 +0000

@vinay,

Please watch this:

http://blogs.mathworks.com/videos/2007/08/31/matlab-basics-video-row-and-column-indexing/

Doug

By: vinay bansal

vinay bansal — Tue, 16 Feb 2010 16:55:04 +0000

thanks for ur kind help sir….. it was really very helpful . i have one more problem sir. thats is as below.

i want to collect data from a matrics . exp:
%a = [ m n p ]%
a = [1 4 61;
1 5 76;
1 6 56
4 1 803;
4 5 500 ;
4 6 865;
5 1 524;
5 4 125;
5 6 265 ;
6 1 57;
6 4 341;
6 5 96];

i want to collect data for m = [1 5 6] n = [1 5 6 ]
means m=1 , n= [ 5 6]
m = 5 , n= [1 6]
m = 6, n= [1 5]
means third column of matrics [a]
will u plz like to tell me how can get it automatically by applying a loop ?

By: dhull

dhull — Thu, 11 Feb 2010 15:08:32 +0000

@vinay,

It is better to make a cell array than to automatically generate variable names in a series like that.

a{1} = [6 4]
a{2} = [8 9; 4 5]

Notice the curly braces.

Doug

By: vinay bansal

vinay bansal — Thu, 11 Feb 2010 14:37:06 +0000

dear sir,
Thanks for your reply . regarding above problem, we have different values of ‘a’ and ‘b’ and ‘n’ is also different for every species(p). means a matrix of n rows and 2 column will come every time from complete running of inner loop. so total 5 matrix will come. exp : [1 3; 5 6]
[6 4 ]
[ 8 9 ; 4 5]
[9 6 ;8 7 ; 5 4]
[8 5; 6 2].
i want to store these matrics…. but when i run this , it show only last matrics… is there any solution to store them like X1,X2,X3,X4,X5 ?