Examples

The following code demonstrates more advanced uses of the Equation Package

Dynamic Ploting of functions

Requires numpy, matplotlib and h5py

sample/DPOF.py

#!/usr/bin/env python
#############################################
# Dynamic Plotting of Function Sample
#############################################
from Equation import Expression
from Equation.core import constants
import matplotlib.pyplot as plt
import numpy as np
import h5py

db = h5py.File("dataset.hdf5", "r") # External Data base of consts and values

while True:
    expr = raw_input("Enter Equation to Plot in terms of (x): ") # Fetch Equation From User Input

    try:
        fn = Expression(expr,['x'])
    except SyntaxError as err:
        print err.message
        continue

    if 'x' not in fn: # check 'x' is used in expr
        print "Error: Equation must have a variable named x"
        continue

    for v in fn: # load all data values from db
        if v == 'x':
            continue
        if v in db:
            fn[v] = db[v]
            continue
        if v in db.attrs:
            fn[v] = db.attrs[v]
            continue
        if v in constants:
            continue
        print "Error: Variable '{0:s}' is not defined in database".format(v)
        break # Break the For Loop
    else:
        break # Break the While Loop

# One We get Here fn is a valid Expression object requiring a single argument 'x'

x = np.linspace(0,1,1000)

plt.plot(x,fn(x))
plt.title("Plot of ${0:s}$".format(fn))
plt.show()

The Following is the result of running the script, given “dataset.hdf5” contains the attribute A = 3

Enter Equation to Plot in terms of (x): A*sin(x*re(sqrt(x-(0.5+0j))))

Enter Equation to Plot in terms of (x): A*sin(x*im(sqrt(x-(0.5+0j))))

This sample asks the user for some function of x and then loads required data from a hdf5 file by search the file for variables in the function the user entered. Once the data has been retrived the function is plotted in the range \([0,1]\) and the plot is titled using the display form of the function the user entered.

Note

It is important to search the hdf5 file for variables as hdf5 files may contain thousands of variables and take several Gigabytes of space.