Creating a matrix with results of while loop

Hi i'm new to MATLAB and was wondering how to plot a two column matrix, one column contianing the count number and the other containing the corresponding uk1 value at each count. Any help would be much appreciated.

%   1)Randomise initial U, m
    Uk0  = rand( 6  , 1 );
    
%   2)initialise iteration process    
    Uk1 = 1;
    Uki = Uk0;

%   3)Begin iterative process
    count = 0 ;
while abs( Uk1 - Uki ) > 10^-9                      
    count = count + 1 ;                   
    Uk1 = inv(Kd) * ( -Kslsu * Uk0 + f ) ;
    Uki = Uk0 ;
    Uk0 = Uk1 ;
end

Answer 1

[Geoff Hayes]

Albert - if you just want to keep track of the Uk1 from each iteration of the loop, then you could do something like

count = 0 ;
Uk1 = 1;
while abs( Uk1(end) - Uki ) > 10^-9                      
    count = count + 1 ;                   
    Uk1(count) = inv(Kd) * ( -Kslsu * Uk0 + f ) ;
    Uki = Uk0 ;
    Uk0 = Uk1(count);
end

You could pre-size the Uk1 array if you know the maximum number of iterations allowed for the while loop....so that you don't get stuck. For example,

maxIterations = 100;
count = 1 ;
Uk1 = zeros(maxIterations, 1);
Uk1(1) = 1;
while abs( Uk1(count) - Uki ) > 10^-9  && count <= maxIterations                                      
    Uk1(count) = inv(Kd) * ( -Kslsu * Uk0 + f ) ;
    Uki = Uk0 ;
    Uk0 = Uk1(count);
    count = count + 1 ; 
end

[Albert Taylor]

Hey Geoff

Thanks for the help, however when implementing the first code you have given me matlab displays an error message. Is there anyway to get around this.

Unable to perform assignment because the left and right sides have a different number of elements.

[Geoff Hayes]

Albert - presumably the error is with the line of code

Uk1(count) = inv(Kd) * ( -Kslsu * Uk0 + f ) ;

If that is the case, then the problem may be because

inv(Kd) * ( -Kslsu * Uk0 + f ) 

is not a scalar and so is an array of two or more elements. Can you confirm that? And if so, does that make sense?

[Geoff Hayes]

Albert's answer moved here

Hey Geoff, thanks again for the reply

inv(Kd) * ( -Kslsu * Uk0 + f )

Is a 6*1 matrix. Is there anyway to fix this ?

[Geoff Hayes]

Albert - it depends how you want to fix this. Should this be a scalar or do you want to keep the 6x1 from each iteration?

[Albert Taylor]

I wish to keep the 6*1 for each iteration

[Geoff Hayes]

If always 6x1, you could do

maxIterations = 100;
count = 1 ;
Uk1 = zeros(6, maxIterations);
Uk1(:,1) = 1;
while abs( Uk1(:,count) - Uki ) > 10^-9  && count <= maxIterations                                      
    Uk1(:,count) = inv(Kd) * ( -Kslsu * Uk0 + f ) ;
    Uki = Uk0 ;
    Uk0 = Uk1(:, count);
    count = count + 1 ; 
end

Note that you might want to adjust your condition

abs( Uk1(:,count) - Uki ) > 10^-9 

since the result of the subtraction is a 6x1 array too.