How to use sinc interpolation

I built a matrix 'sim'

 sim=[];
 for m=1:7
    for n=1:7
        sim(m,n)=m^2+n^2;
    end   
 end

sim =

     2     5    10    17    26    37    50
     5     8    13    20    29    40    53
    10    13    18    25    34    45    58
    17    20    25    32    41    52    65
    26    29    34    41    50    61    74
    37    40    45    52    61    72    85
    50    53    58    65    74    85    98

and I want to use sim(1,:) sim(3,:) sim(5,:) sim(7,:) to interp sim(2,7) by sinc interpolation

There is subroutine

   function f=sincinterp2b(x,y,g,intx,inty)
 f=0;
[mm,nn] = size(g);
for m=mm:-2:1
  for n=1:nn
      switch m
          case 7 
    eq=0;
    eq= g(m,n).*sinc((x/intx)-n).*sinc((y/inty)-1);
          case 6
    eq=0;
    eq= g(m,n).*sinc((x/intx)-n).*sinc((y/inty)-2);
          case 5
    eq=0;
    eq= g(m,n).*sinc((x/intx)-n).*sinc((y/inty)-3);
          case 4
    eq=0;
    eq= g(m,n).*sinc((x/intx)-n).*sinc((y/inty)-4);
          case 3 
    eq=0;
    eq= g(m,n).*sinc((x/intx)-n).*sinc((y/inty)-5);
          case 2
    eq=0;
    eq= g(m,n).*sinc((x/intx)-n).*sinc((y/inty)-6);
          case 1 
    eq=0;
    eq= g(m,n).*sinc((x/intx)-n).*sinc((y/inty)-7);
      end
               f=f + eq;
  end
 end

I use sincinterp2b(6.5,5.5,sim,1,2) to interp sim(2,7). but its answer is wrong. Where is my mistake