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fvn_quadpack/dqk51_2d_inner.f
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! fvn comment :
! Modified version of the dqk51 quadpack routine from http://www.netlib.org/quadpack
!
! + The external 'f' function is a 2 parameters function f(x,y). The routine
! takes one more parameter 'x' and evaluate the integral of f against y between a and b
! for a given x
subroutine dqk51_2d_inner(f,x,a,b,result,abserr,resabs,resasc)
!***begin prologue dqk51
!***date written 800101 (yymmdd)
!***revision date 830518 (yymmdd)
!***category no. h2a1a2
!***keywords 51-point gauss-kronrod rules
!***author piessens,robert,appl. math. & progr. div. - k.u.leuven
! de doncker,elise,appl. math & progr. div. - k.u.leuven
!***purpose to compute i = integral of f over (a,b) with error
! estimate
! j = integral of abs(f) over (a,b)
!***description
!
! integration rules
! standard fortran subroutine
! double precision version
!
! parameters
! on entry
! f - double precision
! function subroutine defining the integrand
! function f(x). the actual name for f needs to be
! declared e x t e r n a l in the calling program.
!
! a - double precision
! lower limit of integration
!
! b - double precision
! upper limit of integration
!
! on return
! result - double precision
! approximation to the integral i
! result is computed by applying the 51-point
! kronrod rule (resk) obtained by optimal addition
! of abscissae to the 25-point gauss rule (resg).
!
! abserr - double precision
! estimate of the modulus of the absolute error,
! which should not exceed abs(i-result)
!
! resabs - double precision
! approximation to the integral j
!
! resasc - double precision
! approximation to the integral of abs(f-i/(b-a))
! over (a,b)
!
!***references (none)
!***routines called d1mach
!***end prologue dqk51
!
double precision a,absc,abserr,b,centr,dabs,dhlgth,dmax1,dmin1, &
epmach,f,fc,fsum,fval1,fval2,fv1,fv2,hlgth,resabs,resasc, &
resg,resk,reskh,result,uflow,wg,wgk,xgk,x
integer j,jtw,jtwm1
external f
!
dimension fv1(25),fv2(25),xgk(26),wgk(26),wg(13)
!
! the abscissae and weights are given for the interval (-1,1).
! because of symmetry only the positive abscissae and their
! corresponding weights are given.
!
! xgk - abscissae of the 51-point kronrod rule
! xgk(2), xgk(4), ... abscissae of the 25-point
! gauss rule
! xgk(1), xgk(3), ... abscissae which are optimally
! added to the 25-point gauss rule
!
! wgk - weights of the 51-point kronrod rule
!
! wg - weights of the 25-point gauss rule
!
!
! gauss quadrature weights and kronron quadrature abscissae and weights
! as evaluated with 80 decimal digit arithmetic by l. w. fullerton,
! bell labs, nov. 1981.
!
data wg ( 1) / 0.011393798501026287947902964113235d0 /
data wg ( 2) / 0.026354986615032137261901815295299d0 /
data wg ( 3) / 0.040939156701306312655623487711646d0 /
data wg ( 4) / 0.054904695975835191925936891540473d0 /
data wg ( 5) / 0.068038333812356917207187185656708d0 /
data wg ( 6) / 0.080140700335001018013234959669111d0 /
data wg ( 7) / 0.091028261982963649811497220702892d0 /
data wg ( 8) / 0.100535949067050644202206890392686d0 /
data wg ( 9) / 0.108519624474263653116093957050117d0 /
data wg ( 10) / 0.114858259145711648339325545869556d0 /
data wg ( 11) / 0.119455763535784772228178126512901d0 /
data wg ( 12) / 0.122242442990310041688959518945852d0 /
data wg ( 13) / 0.123176053726715451203902873079050d0 /
!
data xgk ( 1) / 0.999262104992609834193457486540341d0 /
data xgk ( 2) / 0.995556969790498097908784946893902d0 /
data xgk ( 3) / 0.988035794534077247637331014577406d0 /
data xgk ( 4) / 0.976663921459517511498315386479594d0 /
data xgk ( 5) / 0.961614986425842512418130033660167d0 /
data xgk ( 6) / 0.942974571228974339414011169658471d0 /
data xgk ( 7) / 0.920747115281701561746346084546331d0 /
data xgk ( 8) / 0.894991997878275368851042006782805d0 /
data xgk ( 9) / 0.865847065293275595448996969588340d0 /
data xgk ( 10) / 0.833442628760834001421021108693570d0 /
data xgk ( 11) / 0.797873797998500059410410904994307d0 /
data xgk ( 12) / 0.759259263037357630577282865204361d0 /
data xgk ( 13) / 0.717766406813084388186654079773298d0 /
data xgk ( 14) / 0.673566368473468364485120633247622d0 /
data xgk ( 15) / 0.626810099010317412788122681624518d0 /
data xgk ( 16) / 0.577662930241222967723689841612654d0 /
data xgk ( 17) / 0.526325284334719182599623778158010d0 /
data xgk ( 18) / 0.473002731445714960522182115009192d0 /
data xgk ( 19) / 0.417885382193037748851814394594572d0 /
data xgk ( 20) / 0.361172305809387837735821730127641d0 /
data xgk ( 21) / 0.303089538931107830167478909980339d0 /
data xgk ( 22) / 0.243866883720988432045190362797452d0 /
data xgk ( 23) / 0.183718939421048892015969888759528d0 /
data xgk ( 24) / 0.122864692610710396387359818808037d0 /
data xgk ( 25) / 0.061544483005685078886546392366797d0 /
data xgk ( 26) / 0.000000000000000000000000000000000d0 /
!
data wgk ( 1) / 0.001987383892330315926507851882843d0 /
data wgk ( 2) / 0.005561932135356713758040236901066d0 /
data wgk ( 3) / 0.009473973386174151607207710523655d0 /
data wgk ( 4) / 0.013236229195571674813656405846976d0 /
data wgk ( 5) / 0.016847817709128298231516667536336d0 /
data wgk ( 6) / 0.020435371145882835456568292235939d0 /
data wgk ( 7) / 0.024009945606953216220092489164881d0 /
data wgk ( 8) / 0.027475317587851737802948455517811d0 /
data wgk ( 9) / 0.030792300167387488891109020215229d0 /
data wgk ( 10) / 0.034002130274329337836748795229551d0 /
data wgk ( 11) / 0.037116271483415543560330625367620d0 /
data wgk ( 12) / 0.040083825504032382074839284467076d0 /
data wgk ( 13) / 0.042872845020170049476895792439495d0 /
data wgk ( 14) / 0.045502913049921788909870584752660d0 /
data wgk ( 15) / 0.047982537138836713906392255756915d0 /
data wgk ( 16) / 0.050277679080715671963325259433440d0 /
data wgk ( 17) / 0.052362885806407475864366712137873d0 /
data wgk ( 18) / 0.054251129888545490144543370459876d0 /
data wgk ( 19) / 0.055950811220412317308240686382747d0 /
data wgk ( 20) / 0.057437116361567832853582693939506d0 /
data wgk ( 21) / 0.058689680022394207961974175856788d0 /
data wgk ( 22) / 0.059720340324174059979099291932562d0 /
data wgk ( 23) / 0.060539455376045862945360267517565d0 /
data wgk ( 24) / 0.061128509717053048305859030416293d0 /
data wgk ( 25) / 0.061471189871425316661544131965264d0 /
! note: wgk (26) was calculated from the values of wgk(1..25)
data wgk ( 26) / 0.061580818067832935078759824240066d0 /
!
!
! list of major variables
! -----------------------
!
! centr - mid point of the interval
! hlgth - half-length of the interval
! absc - abscissa
! fval* - function value
! resg - result of the 25-point gauss formula
! resk - result of the 51-point kronrod formula
! reskh - approximation to the mean value of f over (a,b),
! i.e. to i/(b-a)
!
! machine dependent constants
! ---------------------------
!
! epmach is the largest relative spacing.
! uflow is the smallest positive magnitude.
!
!***first executable statement dqk51
epmach = d1mach(4)
uflow = d1mach(1)
!
centr = 0.5d+00*(a+b)
hlgth = 0.5d+00*(b-a)
dhlgth = dabs(hlgth)
!
! compute the 51-point kronrod approximation to
! the integral, and estimate the absolute error.
!
fc = f(x,centr)
resg = wg(13)*fc
resk = wgk(26)*fc
resabs = dabs(resk)
do 10 j=1,12
jtw = j*2
absc = hlgth*xgk(jtw)
fval1 = f(x,centr-absc)
fval2 = f(x,centr+absc)
fv1(jtw) = fval1
fv2(jtw) = fval2
fsum = fval1+fval2
resg = resg+wg(j)*fsum
resk = resk+wgk(jtw)*fsum
resabs = resabs+wgk(jtw)*(dabs(fval1)+dabs(fval2))
10 continue
do 15 j = 1,13
jtwm1 = j*2-1
absc = hlgth*xgk(jtwm1)
fval1 = f(x,centr-absc)
fval2 = f(x,centr+absc)
fv1(jtwm1) = fval1
fv2(jtwm1) = fval2
fsum = fval1+fval2
resk = resk+wgk(jtwm1)*fsum
resabs = resabs+wgk(jtwm1)*(dabs(fval1)+dabs(fval2))
15 continue
reskh = resk*0.5d+00
resasc = wgk(26)*dabs(fc-reskh)
do 20 j=1,25
resasc = resasc+wgk(j)*(dabs(fv1(j)-reskh)+dabs(fv2(j)-reskh))
20 continue
result = resk*hlgth
resabs = resabs*dhlgth
resasc = resasc*dhlgth
abserr = dabs((resk-resg)*hlgth)
if(resasc.ne.0.0d+00.and.abserr.ne.0.0d+00) &
abserr = resasc*dmin1(0.1d+01,(0.2d+03*abserr/resasc)**1.5d+00)
if(resabs.gt.uflow/(0.5d+02*epmach)) abserr = dmax1 &
((epmach*0.5d+02)*resabs,abserr)
return
end subroutine
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