SUBROUTINE PDA_DB2VAL(XVAL,YVAL,IDX,IDY,TX,TY,
: NX,NY,KX,KY,BCOEF,WORK,
: RVALUE,IFAIL,STATUS)
C***BEGIN PROLOGUE DB2VAL
C***DATE WRITTEN 25 MAY 1982
C***REVISION DATE 25 MAY 1982
C***CATEGORY NO. E1A
C***KEYWORDS INTERPOLATION, TWO-DIMENSIONS, GRIDDED DATA, SPLINES,
C PIECEWISE POLYNOMIALS
C***AUTHOR BOISVERT, RONALD, NBS
C SCIENTIFIC COMPUTING DIVISION
C NATIONAL BUREAU OF STANDARDS
C WASHINGTON, DC 20234
C***PURPOSE DB2VAL EVALUATES THE PIECEWISE POLYNOMIAL INTERPOLATING
C FUNCTION CONSTRUCTED BY THE ROUTINE DB2INK OR ONE OF ITS
C PARTIAL DERIVATIVES.
C DOUBLE PRECISION VERSION OF B2VAL.
C***DESCRIPTION
C
C DB2VAL evaluates the tensor product piecewise polynomial
C interpolant constructed by the routine DB2INK or one of its
C derivatives at the point (XVAL,YVAL). To evaluate the interpolant
C itself, set IDX=IDY=0, to evaluate the first partial with respect
C to x, set IDX=1,IDY=0, and so on.
C
C DB2VAL returns 0.0E0 if (XVAL,YVAL) is out of range. That is, if
C XVAL.LT.TX(1) .OR. XVAL.GT.TX(NX+KX) .OR.
C YVAL.LT.TY(1) .OR. YVAL.GT.TY(NY+NY)
C If the knots TX and TY were chosen by DB2INK, then this is
C equivalent to
C XVAL.LT.X(1) .OR. XVAL.GT.X(NX)+EPSX .OR.
C YVAL.LT.Y(1) .OR. YVAL.GT.Y(NY)+EPSY
C where EPSX = 0.1*(X(NX)-X(NX-1)) and EPSY = 0.1*(Y(NY)-Y(NY-1)).
C
C The input quantities TX, TY, NX, NY, KX, KY, and BCOEF should be
C unchanged since the last call of DB2INK.
C
C
C
C I N P U T
C ---------
C
C XVAL Double precision scalar
C X coordinate of evaluation point.
C
C YVAL Double precision scalar
C Y coordinate of evaluation point.
C
C IDX Integer scalar
C X derivative of piecewise polynomial to evaluate.
C
C IDY Integer scalar
C Y derivative of piecewise polynomial to evaluate.
C
C TX Double precision 1D array (size NX+KX)
C Sequence of knots defining the piecewise polynomial in
C the x direction. (Same as in last call to DB2INK.)
C
C TY Double precision 1D array (size NY+KY)
C Sequence of knots defining the piecewise polynomial in
C the y direction. (Same as in last call to DB2INK.)
C
C NX Integer scalar
C The number of interpolation points in x.
C (Same as in last call to DB2INK.)
C
C NY Integer scalar
C The number of interpolation points in y.
C (Same as in last call to DB2INK.)
C
C KX Integer scalar
C Order of polynomial pieces in x.
C (Same as in last call to DB2INK.)
C
C KY Integer scalar
C Order of polynomial pieces in y.
C (Same as in last call to DB2INK.)
C
C BCOEF Double precision 2D array (size NX by NY)
C The B-spline coefficients computed by DB2INK.
C
C WORK Double precision 1D array (size 3*max(KX,KY) + KY)
C A working storage array.
C
C IFAIL A returned error value.
C
C RVALUE The interpolated value.
C
C STATUS Integer. Starlink status report.
C
C***REFERENCES CARL DE BOOR, A PRACTICAL GUIDE TO SPLINES,
C SPRINGER-VERLAG, NEW YORK, 1978.
C***ROUTINES CALLED DINTRV,DBVAL2
C***END PROLOGUE DB2VAL
PDA [1ex