Solving equations with parameters Python fsolve

Question

I am trying to find the zero's of several straight lines solving one of them at a time with fsolve function. I can't manage to write a decent code that will do this, this below is my best attempt so far, any help is very much appreciated. I think the best way to do it is to define a class (the class being the line with its two properties i.e the slope and the y intercept) but I do not know how to do this.

import numpy as np
from scipy.optimize import fsolve


def straight_line(parameters):
    m = parameters[0]             # This is the first parameter of the line i.e the slope
    n = parameters[1]             # This is the second parameter of the line i.e. the y-axis intercept
    x = parameters[3]             # This is the variable of the function, I want to find x such that m * x + n = 0
    return m * x + n


for m in range(-10,10):
    for n in range(-10,10):
        guess = 1
        zero = fsolve(straight_line([m, n]), guess)   # This is not correct
        print([m, n, zero])

What does "This is not correct" mean? What is the output? What do you expect it to be instead? — Code-Apprentice, Jan 11 '21 at 15:49
Hello @Code-Apprentice I mean that the line is not correct (the interpreter will not understand that line). I just wrote it because I think it reflects well what I want the program to do, so it will be useful to explain myself. Inside the nested loops I wanna find the zero of the straight line but in each loop iteration the line parameters (m,n) should change i.e. each time is a different equation I am solving — Miguel Garcia, Jan 11 '21 at 15:57
"the line is not correct" and "the interpreter will not understand that line" still doesn't tell us what happens when you run your code. Please [edit] your question to show the exact output when you run your program. — Code-Apprentice, Jan 11 '21 at 16:03
The problem here is that you are not using `fsolve()` correctly. I suggest you find some tutorials and read the documentation to understand how to correctly call it to do what you want. — Code-Apprentice, Jan 11 '21 at 16:04

Code-Apprentice · Answer 1 · 2021-01-11T16:02:23.870

zero = fsolve(straight_line([m, n]), guess)

The problem is that you call straight_line() and send the calculated value to fsolve. If you read the documentation, you will see that the first parameter to fsolve, must be a "callable". In other words, you need to pass the function itself:

zero = fsolve(straight_line, guess)

You also need to pass the args to define the line, in this case the slope and y-intercept:

zero = fsolve(straight_line, guess, args=(m, n))

Also, you have to make sure the x value is the first parameter to straight_line():

def straight_line(x, m, b):
    return m*x + b

I haven't tested this, so it might not be exactly correct. It might not fix all the problems. I suggest you read more tutorials and examples to learn about how this works. Refer to the documentation to be sure you are using fsolve() correctly.

Solving equations with parameters Python fsolve

1 Answers1

Linked