Having trouble writing an equation with scientific notation and exponents in Python

Question

I am having some trouble writing this equation in Python and having it produce correct results:

y = 2.95710^-7 * x^4 – 2.34310^-5 * x^3 – 1.67*10^-4 * x^2 + 0.04938 * x – 1.083.

I have tried the following code:

y = 0.0000002957*x**4 - 0.00002343*x**3 - 0.000167*x**2 + 0.04938*x - 1.083

and also:

y = (2.957*10**-7)*x**4 - (2.343*10**-5)x**3 - (1.67*10**4)*x**2 + 0.04938*x - 1.083

any advice would be helpful, I think the problem might be the scientific notation or the exponents and the way I am inputting them

EDIT in response to questions, the equation spits out an incorrect number than what I get on a calculator

What trouble are you having? What do you expect it to produce? What does it actually produce? — Pranav Hosangadi, Mar 29 '21 at 16:32
`(2.343*10**-5)x**3` needs to be `(2.343*10**-5)*x**3`, maybe? Also, note that Python understands scientific notation. `2.343e-5` works just as well as `0.00002343` or `2.343*10**-5` — Pranav Hosangadi, Mar 29 '21 at 16:34
@user15108227 **What do you expect it to produce? What does it actually produce?** Please take the [tour], read [what's on-topic here](/help/on-topic), [ask], and the [question checklist](//meta.stackoverflow.com/q/260648/843953), and provide a [mre]. — Pranav Hosangadi, Mar 29 '21 at 16:35
Apart from the `*` before `x**3`, there's also a missing `-` in `(1.67*10**4)`...* — Thierry Lathuille, Mar 29 '21 at 16:41

CryptoFool · Answer 1 · 2021-03-29T17:37:40.117

What you have can easily be converted to Python in a very direct way. The equivalent Python statement (after fixing a flaw in the original equation...see below) is :

y = 2.95710e-7 * x**4 - 2.34310e-5 * x**3 - 1.67e-4 * x**2 + 0.04938 * x - 1.083

This involves only the simple substitution of the ^ characters, where you replace that character with e in the exponential floating point constants and with ** for raising x to an integer power. For reference to be able to more easily compare the source with the result, here's the original equation with the one slight fix mentioned below:

y = 2.95710^-7 * x^4 – 2.34310^-5 * x^3 – 1.67^-4 * x^2 + 0.04938 * x – 1.083

UPDATE: Thanks to Pranav for pointing out a flaw in the source equation. The term 1.67*10^-4 should be changed to 1.67^-4 to match the other similar terms, and the equivalent fix made to the resulting Python equation. Those fixes were made and commented on above.

I always like to see what I'm working with in situations like this. I used matplotlib to plot this function, using an unchanged version (except for the function and the bounds on x) of this sample code. Here's what I got for x values between -500 and 500:

score 0 · Answer 2 · answered Mar 30 '21 at 17:47

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Thanks for answering everybody. The most helpful answer was using "e" instead of scientific notation (*10^x).

answered Mar 30 '21 at 17:47

user15108227

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Having trouble writing an equation with scientific notation and exponents in Python

2 Answers2