c integ.for - return the running integral of an array 
c             using the trapezoidal method
c
      subroutine integ ( nvals, x, y, rInteg )
        implicit real(a-h,o-z)

      dimension  x(*), y(*)
      dimension rInteg( nvals )

ccc      type *, 'j  x(j)  x(j-1)  y(j)  y(j-1)  rInteg(j)'
c
      rInteg(1) = 0.0

      do j = 2, nvals
         rInteg(j) = rInteg(j-1) + (y(j)+y(j-1))/2.*(x(j)-x(j-1))

ccc	if (j .lt. 105) type *, j, x(j),x(j-1),y(j),y(j-1),rInteg(j)
      enddo
      
      return
c
      end