# Questions tagged [equation-solving]

Questions on the analytic and numerical equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).

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### NDSolve is finding a stiff system very quickly trying to solve a large set of differential equations

I'm a physics PhD student solving lubrication equations (non-linear PDEs) related to the evaporation of binary droplets in a cylindrical pixel in order to simulate the shape evolution. So I split the ...
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### How to make sure the answer is limited to Positive Reals?

As the title described, there is code: ...
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### Solving quadratic eqaution with many parameters [closed]

It seems like Mathematica or my PC has problems to handle long equations: ...
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### Incorrect result by DSolve

For real $x$ consider the trivial equation $$|y'(x)|=-|x|.$$ Since the left side is always positive and the right always negative, there is no solution. Let's try ...
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### Solve a linear system using the substitution method [closed]

I know that, for the substitution method, I have to isolate the first variable, plug the equation for that variable into the other equations, simplify the new equations, isolate the second variable, ...
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### NSolve with Bessel and Hankel functions

I have a complicated function that I would like to solve for the roots. The function comprises Bessel and Hankel functions: ...
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### Solving a large system of equations for the smallest integer values

I'm trying to find the smallest possible non-negative integer solutions to hundreds of fairly large equations systems . An average example would be the following: ...
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### Reducing solutions from Solve to positive solutions

Consider the following lines; ...
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### Assuming a monotonic function

I'm trying to tell Mathematica that a function is increasing. More specifically, I would like at least one of the following statements to report 'true'. ...