# DSolveValue error: equations are not the same shape

**URL:** <https://community.wolfram.com/t/dsolvevalue-error-equations-are-not-the-same-shape/19730>\
**Category:** Questions\
**Tags:** calculus, equation-solving, symbolic-computations\
**Created:** [March 7, 2022, 7:07pm UTC](https://community.wolfram.com/t/dsolvevalue-error-equations-are-not-the-same-shape/19730 "2022-03-07T19:07:48Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![sorabella91](https://avatars.discourse-cdn.com/v4/letter/s/ecae2f/32.png) [@sorabella91](https://community.wolfram.com/u/sorabella91)\
**Post date:** [March 7, 2022, 7:07pm UTC](https://community.wolfram.com/t/dsolvevalue-error-equations-are-not-the-same-shape/19730/1 "2022-03-07T19:07:48Z")

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Hello,

I have a system of differential equations that can be used to model orbits of stars in binary systems in cartesian coordinates. Normally, I specify the masses of the stars, the period and eccentricity of the orbit to use for initial conditions, I use NDSolveValue and things work great. However, I want to solve the functions symbolically where I do not give initial conditions for the masses of the two stars and, instead get a solution that is mass dependent. I switched to DSolveValue, keeping all of the diff eqs the same and just didn’t specify what the masses were. However, I keep getting an error message saying that things are not the same shape. Is it possible to solve these diff eqs without specifying the mass of the two stars?

[Open in Wolfram Cloud ↗](https://www.wolframcloud.com/obj/56996e41-1783-409e-9e48-11481dceb20d)

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<div class="post-metadata">

**Author:** ![gianlucagorni](https://avatars.discourse-cdn.com/v4/letter/g/ec9cab/32.png) [@gianlucagorni](https://community.wolfram.com/u/gianlucagorni)\
**Post date:** [March 7, 2022, 8:22pm UTC](https://community.wolfram.com/t/dsolvevalue-error-equations-are-not-the-same-shape/19730/2 "2022-03-07T20:22:19Z")

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You should not use `Period`, because it is a built-in symbol.

Mathematica cannot find an analytical solution to your equations. The opaque error message is just a consequence of that.

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<div class="post-metadata">

**Author:** ![sorabella91](https://avatars.discourse-cdn.com/v4/letter/s/ecae2f/32.png) [@sorabella91](https://community.wolfram.com/u/sorabella91)\
**Post date:** [March 7, 2022, 9:43pm UTC](https://community.wolfram.com/t/dsolvevalue-error-equations-are-not-the-same-shape/19730/3 "2022-03-07T21:43:55Z")

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If an analytical solution does not exist, would it be possible to solve it numerically without specifying the masses? NDSolveValue does work if mass is specified but doesn’t seem to like when mass is not given an actual value to it. Any work arounds?