# RIDGEINTERP is the jRidges module of jLab.

```  RIDGEINTERP  Interpolate quantity values onto ridge locations.

RIDGEINTERP is a low-level function called by RIDGEWALK.

XI=RIDGEINTERP(FS,RQ,IR,JR,X) where RQ is a "ridge quantity" at
*radian* frequencies FS, and IR and JR are time and scale indices of
ridges, interpolates quantity X along the ridge locations to give XI.

IR and JR give indices into the first two dimensions of X.  The output
XI has the the same number of rows and columns as IR and JR, that is,
SIZE(XI,1)=SIZE(IR,1) and SIZE(XI,2)=SIZE(IR,2).  The locations of
NANs in IR and JR are duplicated in XI.

X may have more than one 'page' along its third dimension, in which
case each page is interpolated separately, and SIZE(XI,3)=SIZE(X,3).

RQ is output by ISRIDGEPOINT based on a wavelet transform output by
WAVETRANS, and IR and JR are output by RIDGEWALK.

RIDGEINTERP interpolates transform values between discrete frequency
levels to find a more precise value of the transform along the ridges
than simply looking up the values of X at rows IR and columns JR.

XI=RIDGEINTERP(FS,RQ,IR,JR,MU,X) interprets the ridges as belonging
to the MU-th derivative of the signal to which the quantity X belongs
and applies an appropriate correction factor.

[XI1,XI2,...,XIN]=RIDGEINTERP(FS,RQ,IR,JR,X1,X2,...,XN) also
interpolates the quantities X1,X2,...,XN, all having the same number of
rows and columns as IR and JR.

cases, quadratic interpolation fails for an individual point and
therefore linear interpolation is used instead.
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RIDGEINTERP is a low-level function called by RIDGEWALK.