Why is this ending my matrices before they are filled, and how do I print the answer of the multiplication?

C=input('How many columns are there in P?  ');
    R=input('How many rows are there in P?  ');
    P=zeros(R:C);
    co=1; 
    ro=1;
          while co<=C+1 && ro<=R+1;
              
                  P(co)=input('What is the first value of this column of P? ')
                  co=co+1;
              
                  P(co)=input('What is the next value of this column of P?  ')
                  co=co+1;
              
              ro=ro+1;
          end 
      

B=input('How many columns are there in D?  ');
    T=input('How many rows are there in D?  ');
    D=zeros(R:C);
    co=1; 
    ro=1;
          while co<=C+1 && ro<=R+1;
              
                  D(co)=input('What is the first value of this column of D? ')
                  co=co+1;
              
                  D(co)=input('What is the next value of this column of D?  ')
                  co=co+1;
              
              ro=ro+1;
          end 

V = P*D; 
Print(V)

When entering the values of the matrices if I make it more than 2 columns it puts zeros in for the 3rd and subsequent columns. I'm also trying to print (not sure what the command is in matlab) V, to have the value show. However using print it searches my hard drive to try and find a file (which is odd since I'm not using open).

I would assume if the matrices aren't able to be multiplied and error message shows up, but is there a way to make that a dialogue box?

[Steven Lord]

%{
 P=zeros(R:C);
%}

This doesn't do what you want.

R = 5;
C = 2;
P1 = zeros(R:C)

P1 =

     []

P2 = zeros(R,C)

P2 = 5×2

0 0 0 0 0 0 0 0 0 0

The expression 5:2 returns the empty array. When you pass that into zeros as the size input you get a 0-by-0. But even worse, if C was much larger than R at best MATLAB would tell you you can't make that large an array. At worst it would try and potentially take a long time to allocate.

R = 2;
C = 30;
numElements = prod(R:C)

numElements = 2.6525e+32

P = zeros(R:C)

Error using zeros
Requested array exceeds the maximum possible variable size.

You can't make a 2-by-3-by-4-by-5-by-6-by-...-by-29-by-30 array because it would have over 2e32 elements.

Answer 1

[Walter Roberson]

print() of a value is Python. MATLAB uses disp()

To make a dialog box for that error:

try
  V = P*D;
catch ME
  errordlg(getReport(ME)) ;
end

[Walter Roberson]

"Why is this ending my matrices before they are filled"

 D=zeros(R:C);

zeros(R:C) means

if C<R
  let D be an empty array of double precision zeros 
elseif R is the same as C
  let D be a square double precision array with R rows and columns 
else
  construct a vector starting from R and adding one each time, ending with the last value that does not exceed C. Now create a double precision array that uses those values as the size of each dimension. So R rows, R+1 columns, R+2 pages, R+3 hyperplanes, and so on to the last entry in the vector.

If the intent was to create an array with R rows and C columns then zeros(R, C)

[David Scidmore]

Got it,

My intent is to let users form what ever size matrix they wish and fill it with their own values. I thought the zeros would clear out the matrix to be filled.

Like they want P to be a 3*5 Matrix they enter the values they want and T could be a 5*3 matrix and they enter the values they wish. Not to be a zero matrix.

My new code only puts everything in a single row.

C=input('How many columns are there in P?  ');
R=input('How many rows are there in P?  ');
    P=(R:C);
    co=1; 
    ro=1;
          while co<=C+1 && ro<=R+1;
              
                  P(co)=input('What is the first value of this column of P? ')
                  co=co+1;
              
                  P(co)=input('What is the next value of this column of P?  ')
                  ro=ro+1;
              
              ro=ro+1;
          end 

[Stephen23]

"I thought the zeros would clear out the matrix to be filled."

Sure, it would.

But you are missing the difference between

zeros(A:B) % what you did (colon does not give the required input to ZEROS)

and

zeros(A,B) % what you need (comma defines two separate inputs)

"My new code only puts everything in a single row."

Because that is what you told MATLAB to do:

P = (R:C) % output is always a row vector