#!/usr/bin/env python
# -*- coding: utf-8 -*-
# written by Christoph Federrath

# define imports
from cfpack.defaults import *
import cfpack as cfp
import numpy as np


# === Amdahl's Law ===
def amdahl(ncores, parallel_fraction):
    serial_fraction = 1 - parallel_fraction
    speedup = 1 / (parallel_fraction / ncores + serial_fraction)
    return speedup


# ===== the following applies in case we are running this in script mode =====
if __name__ == "__main__":

    # number of cores
    ncores = np.array([2**x for x in range(16)])

    # parallel fractions
    parallel_fractions = [0.25, 0.5, 0.9, 0.95]

    # loop over parallel fraction cases
    for pf in parallel_fractions:

        # compute Amdahl's law
        speedup = amdahl(ncores, pf)

        # plot
        cfp.plot(x=ncores, y=speedup, label=r"$P="+cfp.round(pf, 2, True)+r"$")

    # create final plot
    cfp.plot(xlog=True, xlabel="Number of processor cores", ylabel="Speed-up factor", xlim=[0.5, 1e5], ylim=[0, 25], show=True, save="Amdahl.pdf")