bcuint.for

Numerical Recipes一书中例子的源码所用到的函数集,William H. Press 和 Saul A. Teukolsky 所著

      SUBROUTINE bcuint(y,y1,y2,y12,x1l,x1u,x2l,x2u,x1,x2,ansy,ansy1,
     *ansy2)
      REAL ansy,ansy1,ansy2,x1,x1l,x1u,x2,x2l,x2u,y(4),y1(4),y12(4),
     *y2(4)
CU    USES bcucof
      INTEGER i
      REAL t,u,c(4,4)
      call bcucof(y,y1,y2,y12,x1u-x1l,x2u-x2l,c)
      if(x1u.eq.x1l.or.x2u.eq.x2l)pause 'bad input in bcuint'
      t=(x1-x1l)/(x1u-x1l)
      u=(x2-x2l)/(x2u-x2l)
      ansy=0.
      ansy2=0.
      ansy1=0.
      do 11 i=4,1,-1
        ansy=t*ansy+((c(i,4)*u+c(i,3))*u+c(i,2))*u+c(i,1)
        ansy2=t*ansy2+(3.*c(i,4)*u+2.*c(i,3))*u+c(i,2)
        ansy1=u*ansy1+(3.*c(4,i)*t+2.*c(3,i))*t+c(2,i)
11    continue
      ansy1=ansy1/(x1u-x1l)
      ansy2=ansy2/(x2u-x2l)
      return
      END