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stepi.f
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1  REAL*8 FUNCTION stepi(F,FDOT,F2DOT,F3DOT,ETA)
2 *
3 *
4 * Fast time-step expression.
5 * --------------------------
6 *
7  IMPLICIT REAL*8 (a-h,o-z)
8  REAL*8 f(3),fdot(3),f2dot(3),f3dot(3)
9 *
10 *
11 * Set square FDOT & F2DOT and sum of all absolute values.
12  fd2 = fdot(1)**2 + fdot(2)**2 + fdot(3)**2
13  f2d2 = f2dot(1)**2 + f2dot(2)**2 + f2dot(3)**2
14  fi = abs(f(1)) + abs(f(2)) + abs(f(3))
15  fd = abs(fdot(1)) + abs(fdot(2)) + abs(fdot(3))
16  f2d = abs(f2dot(1)) + abs(f2dot(2)) + abs(f2dot(3))
17  f3d = abs(f3dot(1)) + abs(f3dot(2)) + abs(f3dot(3))
18 *
19 * Obtain time-step by simplified relative criterion.
20  stepi = eta*(2.0*fi*f2d + fd2)/(2.0*fd*f3d + f2d2)
21  stepi = sqrt(stepi)
22 *
23  RETURN
24 *
25  END