Why is the Second to Last Sample Off Scale in My Cubic Spline Boundary Problem?

[bwhitejr]

Hi All,
I am trying to convert a file that has three arrays of 528 samples into three arrays of 301.
The first is log spaced frequency points the second is the impedance values at each frequency and the last is phase values. I have the routines spline and splint. My problem is the the second to last sample [299] is off scale. The last sample [300] is correct. I know it is some kind of boundary problem, but it is beyond me to figure it out.

fr,re,ph are arrays[1..528] of float

Spline(fr,re,528,re[1],re[528],y2);
Spline(fr,ph,528,ph[1],ph[528],y4);
fm:=Power((20000.0/10.0),1.0/300);
For i:=1 to 301 do
begin
tempARRF:=10.0*Power(fm,i-1);
end;
For i:=1 to 301 do
begin
splint(fr,re,y2,528,tempARRF,tempARRR);
splint(fr,ph,y4,528,tempARRF,tempARRP);
end;
CloseFile(impFile);
For i:=0 to 300 do
begin
impARR.Freq:=tempARRF[i+1];
impARR.Res:=tempARRR[i+1];
impARR.Phs:=tempARRP[i+1];
end;

 

[Future Bruno]

You could try using the interpolation method to convert the 528 samples into 301. Interpolation works by taking the two closest points and then using a formula to calculate the values for the points in between. For example, if you have two points (x1,y1) and (x2,y2), and you want to calculate the value of y at x, you can use the following formula: y = y1 + (x - x1)(y2 - y1)/(x2 - x1)You can apply this formula to the three arrays of 528 samples to calculate the three arrays of 301 samples.