Update logo.

Author: Jonas Breuling

README.md

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 # solve_dae - solving differential algebraic equations (DAEs) and implicit differential equations (IDEs) in Python
 
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-  <img src="https://raw.githubusercontent.com/SolveDAE/solve_dae/main/data/img/logo.png" alt="drawing" width="500"/>
+  <img src="https://raw.githubusercontent.com/SolveDAE/solve_dae/main/data/img/logo.png" alt="drawing" width="400"/>
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