Question

I am trying to write a data calculated from this function in a file. But the function is called number of times. Say there are 9 numbers in another file and this function will calculate the root for each of those 9 numbers. These 9 roots from this function should be written in the same file. But the way I have done it here will write calculated root in the file but the next one will replace this in the file. There are other mathematical functions that are carried out for each of those 9 numbers before this function is called therefore the functions are called again and again separately.Is it possible to write them all in the same file? Thank you.

def Newton(poly, start):
    """ Newton's method for finding the roots of a polynomial."""
    x = start 
    poly_diff = poly_differentiate(poly)
    n = 1
    counter = 0
    r_i = 0

    cFile = open("curve.dat", "w")   
    while True:
        if (n >= 0) and (n < 1):
            break

        x_n = x - (float(poly_substitute(poly, x)) / poly_substitute(poly_diff, x))

        if x_n == x:
            break

        x = x_n # this is the u value corresponding to the given time

        n -= 1
        counter += 1
        x = str(x)
        cFile.write('\n' + x + '\n')

    if r_i:
        print "t(u) = ", (x, counter)

    else:
        print "t(u) = ", x


    cFile.close 

After following the suggestions I got I changed the code to the following:

def Newton(poly, start):
    """ Newton's method for finding the roots of a polynomial."""
    x = start 
    poly_diff = poly_differentiate(poly)
    n = 1
    counter = 0

    while True:
        if (n >= 0) and (n < 1):
            break

        x_n = x - (float(poly_substitute(poly, x)) / poly_substitute(poly_diff, x))

        if x_n == x:
            break

        x = x_n # this is the u value corresponding to the given time

        n -= 1
        counter += 1
        yield x 

    Bezier(x)

def Bezier(u_value) :
    """ Calculating sampling points using rational bezier curve equation"""
    u = u_value

    p_u = math.pow(1 - u, 3) * 0.7 + 3 * u * math.pow(1 - u, 2) * 0.23 \
        + 3 * (1 - u) * math.pow(u, 2) * 0.1 + math.pow(u, 3) * 0.52

    p_u = p_u * w

    d = math.pow(1 - u, 3) * w + 3 * u * w * math.pow(1 - u, 2) + 3 * (1 - u) *\ 
        w * math.pow(u, 2) + math.pow(u, 3) * w

    p_u = p_u / d

    yield p_u

    plist = list (p_u)
    print plist

I followed the same thing in the Bezier() function but plist is not created as it doesn’t print anything. Please help. Thank you.

Answer 1

Your function does two things: It calculates the roots of a polynomial, and it writes the result to an output file. Functions should ideally do one thing.

So, try breaking this up into a function that receives a polynomial and returns a list containing the roots, and then just write that list to a file in one step.

The simplest way to modify your function would be to replace the lines

x = str(x)
cFile.write('\n' + x + '\n')

with

yield x

Then you can call your function like this:

roots = list(Newton(polynomial, start))

To understand this, read about generators. To write the resulting list to a file, you can use this code:

with open("curve.dat", "w") as output_file:
    output_file.write("\n".join(str(x) for x in roots)