MATLAB: Help to find the mistake in the code, or tell me what’s wrong.

interpolationMATLAB

So here's code:
clc
clear
T0 = [5; 7.5; 10; 12.5; 15; 17.5; 20; 22.5; 25; 27.5; 30];
h0 = [3.3; 7.5; 41.8; 51.8; 61; 101.1; 132.9; 145.5; 171.4; 225.8; 360];
T = 5:0.5:30;
[m n] = size (T);
i=1;
for j=1:n
    if T(1,j)<=T0(i+1,1)
    h(j,1)=h0(i,1)+ ((h0(i+1,1)-h0(i,1))/(T0(i+1,1)-T0(i,1)))*(T(1,j)-T0(i,1));
    fprintf(' %11.5f %11.5f\n',T(1,j), h(j,1))
      end
      if T(1,j)>T0(i+1,1)
          i=i+1;
      end
  end
  plot(T,h)
What I doing here is linear interpolation. Code works fine, and it even print everything out:
       5.00000     3.30000
       5.50000     4.14000
       6.00000     4.98000
       6.50000     5.82000
       7.00000     6.66000
       7.50000     7.50000
       8.50000    21.22000
       9.00000    28.08000
       9.50000    34.94000
      10.00000    41.80000
      11.00000    45.80000
      11.50000    47.80000
      12.00000    49.80000
      12.50000    51.80000
      13.50000    55.48000
      14.00000    57.32000
      14.50000    59.16000
      15.00000    61.00000
      16.00000    77.04000
      16.50000    85.06000
      17.00000    93.08000
      17.50000   101.10000
      18.50000   113.82000
      19.00000   120.18000
      19.50000   126.54000
      20.00000   132.90000
      21.00000   137.94000
      21.50000   140.46000
      22.00000   142.98000
      22.50000   145.50000
      23.50000   155.86000
      24.00000   161.04000
      24.50000   166.22000
      25.00000   171.40000
      26.00000   193.16000
      26.50000   204.04000
      27.00000   214.92000
      27.50000   225.80000
      28.50000   279.48000
      29.00000   306.32000
      29.50000   333.16000
      30.00000   360.00000
but when I print out h at the end of the code it's like this:
      3.3000
      4.1400
      4.9800
      5.8200
      6.6600
      7.5000
           0
     21.2200
     28.0800
     34.9400
     41.8000
           0
     45.8000
     47.8000
     49.8000
     51.8000
           0
     55.4800
     57.3200
     59.1600
     61.0000
           0
     77.0400
     85.0600
     93.0800
    101.1000
           0
    113.8200
    120.1800
    126.5400
    132.9000
           0
    137.9400
    140.4600
    142.9800
    145.5000
           0
    155.8600
    161.0400
    166.2200
    171.4000
           0
    193.1600
    204.0400
    214.9200
    225.8000
           0
    279.4800
    306.3200
    333.1600
    360.0000
where does those zeros appear from? Any ideas?
Thank you in advance 🙂

Best Answer

clc
clear
T0 = [5; 7.5; 10; 12.5; 15; 17.5; 20; 22.5; 25; 27.5; 30];
h0 = [3.3; 7.5; 41.8; 51.8; 61; 101.1; 132.9; 145.5; 171.4; 225.8; 360];
T = 5:0.5:30;
[m n] = size (T);
i=1;
for j=1:n
    if T(1,j)<=T0(i+1,1),
        h(j,1)=h0(i,1)+ ((h0(i+1,1)-h0(i,1))/(T0(i+1,1)-T0(i,1)))*(T(1,j)-T0(i,1));
        fprintf(' %11.5f %11.5f\n',T(1,j), h(j,1));
    end
    if T(1,j)>=T0(i+1,1) %%%%%>= instead >
        i=i+1;
    end
end
plot(T,h)
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