CODEWITHSUNDEEP
python
Ryan Franz
Ryan Franz

Reputation: 133

Is there a way to have a mathematical function as the argument of a function in Python 3?

How can I include a mathematical function as an argument of a function in Python?

In my particular case, I'm writing a Riemann sum calculator that would ideally look like:

def riemann_sum(func_x, minvalue, maxvalue, partitions)
...
return riemannSum

where func_x is some function of x so that I could find the riemann sum of any arbitrary function this:

func_x = x**2
minvalue = 1
maxvalue = 2
partitions = 100
a = riemann_sum(func_x,minvalue,maxvalue,partitions)
print(a)

However, I can't do the above procedure because x is undefined.

I can get the Riemann sum for particular functions of x by manually typing it in to a line of my function that looks like:

someList = [x**2 for x in someOtherList]

Here, the function is x**2, but I can't change it without physically going in and changing the function.

My only solution right now is to define a new Riemann sum function every time I want to find the definite integral of a new function, which works but I feel like there's a better way.

(Edit: My question is different from the Riemann sum question marked as a possible duplicate. Their question is about an implementation specifically for a Riemann sum. My question is about how to incorporate a math function as the argument of a function, and I happen to use Riemann sum as a particular example)

Upvotes: 2

Views: 205

Answers (3)

user5651771
user5651771

Reputation:

I had a similar problem a few years back when I was coding something for my differential equations class. Here is an example of what worked for me:

func_x = "(x**2)+x+1"
paramList = [(1+(1/k),(1/k)-(1/(k+1))) for k in range(1,101)]
# paramList holds the tuple (x,changeInX) for the riemann sum
def riemann_sum(str_func_x,paramList):
    theSum=0
    for tup in paramList:
        x=tup[0]
        diff=tup[1]
        theSum+=eval(str_func_x)*diff
    return theSum
riemannSumValue = riemann_sum(func_x,paramList)

Make sure that param list is really from 1,1+1/100, . . ., 2 for the first index of the tuples in paramList. . . I think it is from 1.01 to 2 as it is now (I took some tylenol pm 20 minutes ago and now I am too tired to check myself.)

Upvotes: 0

tom10
tom10

Reputation: 69182

In Python functions are first class objects so you can, for example, pass functions as arguments to other functions. That is, the way you wrote your riemann_sum function declaration is fine.

What doesn't work is your definition of func_x, since you need to define func_x as a function. For that you can either do:

func_x = lambda x: x**2

or, for a more general multiline (or single line) function

def func_x(x):
    temp = x**2  # just to stretch this out to another line for demonstration
    return temp

Then you can say something like:

def riemann_sum(func_x, minvalue, maxvalue, partitions):
    # below just demos calling func_x, and is a bad way to do the sum
    riemannSum = 0
    step = 1.0*(maxvalue-minvalue)/partitions
    value = minvalue
    while value<maxvalue:
        riemannSum == step*func_x(value)  # here's where func_x is called
        value += step
    return riemannSum

That is, the main point here is that is demonstrates how to call func_x within the riemann_sum function. This allows you to evaluate func_x at different x-values, as required to evaluate the sum.

Upvotes: 1

Wboy
Wboy

Reputation: 2542

# Replace with whatever your function is  
def func_x(x):
    return x**2


def riemann_sum(func_x(3), minvalue, maxvalue, partitions)
...
return riemannSum

This should do it. You can create the function elsewhere, then initialize it in your riemann_sum as an input.

Upvotes: 0

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