intyd.f
SUBROUTINE INTYD (T, K, YH, NYH, DKY, IFLAG)
C***BEGIN PROLOGUE INTYD
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Warning: this routine is not intended to be user-callable.
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C***SUBSIDIARY
C***PURPOSE Subsidiary to DEBDF
C***LIBRARY SLATEC
C***TYPE SINGLE PRECISION (INTYD-S, DINTYD-D)
C***AUTHOR Watts, H. A., (SNLA)
C***DESCRIPTION
C
C INTYD approximates the solution and derivatives at T by polynomial
C interpolation. Must be used in conjunction with the integrator
C package DEBDF.
C ----------------------------------------------------------------------
C INTYD computes interpolated values of the K-th derivative of the
C dependent variable vector Y, and stores it in DKY.
C This routine is called by DEBDF with K = 0,1 and T = TOUT, but may
C also be called by the user for any K up to the current order.
C (see detailed instructions in LSODE usage documentation.)
C ----------------------------------------------------------------------
C The computed values in DKY are gotten by interpolation using the
C Nordsieck history array YH. This array corresponds uniquely to a
C vector-valued polynomial of degree NQCUR or less, and DKY is set
C to the K-th derivative of this polynomial at T.
C The formula for DKY is..
C Q
C DKY(I) = sum C(J,K) * (T - TN)**(J-K) * H**(-J) * YH(I,J+1)
C J=K
C where C(J,K) = J*(J-1)*...*(J-K+1), Q = NQCUR, TN = TCUR, H = HCUR.
C The quantities NQ = NQCUR, L = NQ+1, N = NEQ, TN, and H are
C communicated by common. The above sum is done in reverse order.
C IFLAG is returned negative if either K or T is out of bounds.
C ----------------------------------------------------------------------
C
C***SEE ALSO DEBDF
C***ROUTINES CALLED (NONE)
C***COMMON BLOCKS DEBDF1
C***REVISION HISTORY (YYMMDD)
C 800901 DATE WRITTEN
C 890531 Changed all specific intrinsics to generic. (WRB)
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 900328 Added TYPE section. (WRB)
C 910722 Updated AUTHOR section. (ALS)
C***END PROLOGUE INTYD