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#-----------------------------------------------------------------------

# bisection.py

#-----------------------------------------------------------------------

import sys

import stdio

import gaussian

#-----------------------------------------------------------------------

# Return a float within the interval (lo, hi) for which f(x) is equal

# to y within precision delta.

def invert(f, y, lo, hi, delta=0.00000001):

mid = (lo + hi) / 2.0

if (hi - lo) < delta:

return mid

if f(mid) > y:

return invert(f, y, lo, mid, delta)

else:

return invert(f, y, mid, hi, delta)

#-----------------------------------------------------------------------

# Accept float command-line argument y. Compute and write to

# standard output the value of x for which gaussian.cdf(x) = y.

def main():

y = float(sys.argv[1])

x = invert(gaussian.cdf, y, -8.0, 8.0)

stdio.writef('%.3f\n', x)

if __name__ == '__main__':

main()

#-----------------------------------------------------------------------

# python bisection.py .5

# 0.000

# python bisection.py .95

# 1.645

# python bisection.py .975

# 1.960