Suppose I have a matrix of size(3,3).This is up-scaled by 2 making it (6,6).So there would be a number of vacant values between each element of the initial (3,3) matrix.Then how do you fill up the 0 values in addmatrixR by bicubic/liner interpolation

prevR=magic(3)

m=1;
   k1=1
addRmatrix= zeros(2*size(prevR,1),2*size(prevR,2))

      for i=1:size(prevR,1);
          for j=1:size(prevR,2);
          addRmatrix(m,k1)= prevR(i,j); 
          k1=k1+2   ; 
          end
      m=m+2;
      k1=1;
      end

Answer 1

[Stephen23]

Just use interp2:

>> M = magic(3)
M =
   8   1   6
   3   5   7
   4   9   2
>> interp2(M,1)
ans =
   8.0000   4.5000   1.0000   3.5000   6.0000
   5.5000   4.2500   3.0000   4.7500   6.5000
   3.0000   4.0000   5.0000   6.0000   7.0000
   3.5000   5.2500   7.0000   5.7500   4.5000
   4.0000   6.5000   9.0000   5.5000   2.0000

Or the simplest of all:

>> interp2(M)
ans =
   8.0000   4.5000   1.0000   3.5000   6.0000
   5.5000   4.2500   3.0000   4.7500   6.5000
   3.0000   4.0000   5.0000   6.0000   7.0000
   3.5000   5.2500   7.0000   5.7500   4.5000
   4.0000   6.5000   9.0000   5.5000   2.0000

If you need to specify the sample points, then do something like this:

>> [Xi,Yi] = meshgrid(1:1.0:S(2),1:1.0:S(1));
>> [Xo,Yo] = meshgrid(1:0.5:S(2),1:0.5:S(1));
>> out = interp2(Xi,Yi, M, Xo,Yo)
out =
   8.0000   4.5000   1.0000   3.5000   6.0000
   5.5000   4.2500   3.0000   4.7500   6.5000
   3.0000   4.0000   5.0000   6.0000   7.0000
   3.5000   5.2500   7.0000   5.7500   4.5000
   4.0000   6.5000   9.0000   5.5000   2.0000

[MSP]

But for practical cases the addRmatrix say isnt exactly double dimension,Then what to do.How do we have addRmatrix of dimension 7*8.

[Stephen23]

@MSP: all of the solutions I gave will automatically adjust for the matrix size. Try them!

[MSP]

Thanks a lot,But could you elaborate the third code for me. What does Xo and Yo specify

[Stephen23]

@MSP: Xi and Yi are sample locations of the input data values: I defined these arbitrarily to be with steps of one. Xo and Yo are the sample locations of the output data values: I defined these to have half the step size of the input steps (steps of 0.5).

Answer 2

[C.J. Harris]

Just use interp2 on the original matrix, like so:

prevR = magic(3)
ans =

       8     1     6
       3     5     7
       4     9     2

addRmatrix = interp2(prevR,1)
ans =

    8.0000    4.5000    1.0000    3.5000    6.0000
    5.5000    4.2500    3.0000    4.7500    6.5000
    3.0000    4.0000    5.0000    6.0000    7.0000
    3.5000    5.2500    7.0000    5.7500    4.5000
    4.0000    6.5000    9.0000    5.5000    2.0000

[MSP]

But for practical cases the addRmatrix say isnt exactly double dimension,Then what to do.How do we have addRmatrix of dimension 7*8.