.help msider Dec98 "Image Interpolation Package"
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NAME
msider -- evaluate the interpolant derivatives at x and y 
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SYNOPSIS
msider (msi, x, y, der, nxder, nyder, len_der)

.nf
    pointer	msi			#I interpolant descriptor
    real	x[4]			#I x value, 1 <= x[1-4] <= nxpix
    real	y[4]			#I y value, 1 <= y[1-4] <= nypix
    real	der[len_der, ARB]	#O derivative array
    int		nxder			#I number of x derivatives
    int		nyder			#I number of y derivatives
    int		len_der			#I row length of der, len_der >= nxder
.fi
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ARGUMENTS
.ls msi
Pointer to the 2D sequential interpolant descriptor.
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.ls x, y
The single x and y values or in the case of the drizzle interpolant the
single quadrilateral at / over which the point is to be evaluated.
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.ls der
The array containing the derivatives. Der[1,1] contains the value of
the interpolant at x and y. Der[2,1] and der[1,2] contain the 1st
derivatives of x and y respectively.
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.ls nxder, nyder
The number derivatives in x and y.
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.ls len_der
The row length of der. Len_der must be >= nxder.
.le
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DESCRIPTION
The polynomial and spline interpolants are evaluated using the polynomial
coefficients and nested multiplication. The polynomial interpolants are
stored as the data points. The spline interpolant is stored as a set of
B-spline coefficients.
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NOTES
MRIDER checks that the number of derivatives requested is reasonable.
Checking for out of bounds and INDEF valued pixels is the responsibility of the
user. MSIINIT and MSIFIT must be called before using MSIDER.
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SEE ALSO
mrider
.endhelp