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spline - Script command

FDTD MODE DGTD CHARGE HEAT FEEM INTERCONNECT

Does a cubic spline interpolation of a data set.

Syntax

Description

out = spline(Ex,xold,xnew);

"not-a-knot" cubic spline interpolation of a 1D function.

  • Ex is an existing data set
  • xold specifies the points where Ex is sampled
  • xnew specifies new points to interpolate the data.

The points in xnew do not have to be within the bounds of xold.

spline(Ex,xold,xnew,[derivMin; derivMax]);

 "clamped cubic spline" interpolation of a 1D function.

  • Ex is an existing data set
  • xold specifies the points where Ex is sampled
  • xnew specifies new points to interpolate the data.
  • derivMin specifies the 1st-order derivatives at the starting point
  • derivMax specifies the 1st-order derivatives at the ending point

Note: "spline" script has been modified for versions of 2020 R2 or higher. To recover the result from previous versions, users will need to explicitly use the "clamped cubic spline". eg, define

derivMin = (Ex(2)-Ex(1))/(xold(2)-xold(1));

derivMax = (Ex(end)-Ex(end-1))/(xold(end)-xold(end-1));

 

Example

Resample Ex at xnew using cubic spline and linear interpolation methods. Note that xnew is outside the bounds of xold.

xold=linspace(0,10,7);
Ex=sin(xold);
xnew=linspace(-1,9,25); # defining a new x vector
Exnew=interp(Ex,xold,xnew); # interpolating the new data set
Exnew2=spline(Ex,xold,xnew); # smoothing
plotxy(xold,Ex,xnew,Exnew,xnew,Exnew2,"x","y","");
legend("old data", "interp", "Spline");

The example code will generate the plot below. The figure shows the difference between the linear and cubic spline interpolation techniques.

 

See Also

List of commands , interp , plotxy

Associated files

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