**CIGAL Reference Manual, Chapter 3 (Functions): interpolate**
===== Interpolate -- Calculate intermediate values based on a standard curve =====
**usage: y = interpolate(x,stdx,stdy,flag)**

INTERPOLATE uses a standard curve, defined by the two arrays STDX and STDY,
which convert a third set of values, X, to output values Y.  The conversion
involves first finding the STDX values on either side of each X value (or
the two nearest values if X is outside the range of STDX). The Y values are
then generated based on the STDY values corresponding to those nearest STDX
values. INTERPOLATE normally does a linear local interpolation of Y values
based on a standard curve that need not be linear. This type of interpolation
can be modified by using the FLAG option as:
                   FLAG:  0 - linear interpolation (default)
                          1 - set Y2 to the STDY value corresponding to the closest STDX
                                  value that is at or below X2
                          2 - set Y2 to the STDX value corresponding to the closest STDX
                                  value that is at or below X2
                          3 - do a cubic spline interpolation instead of a simple linear
                                  interpolation
                          4 - fill Y2 with linearly increasing values (e.g. 0,1,2,...) 
                                  with the counting base reset to the STDY value each time 
                                  the X value crosses one of the STDX values

The length of the arrays STDX and STDY must be the same.  The number of Y
output values generated will be the same as the number of X input values.

**See Also:**\\
[[jvs:cigal:manual:chapter2:spline|SPLINE(2)]]

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