[fredroy]

MatrixLinearSystem builds the matrices of the components in the order of their addresses (maps keyed by pointers): the rounding of the sums of contributions to the same entries changes with the memory layout, from one run to another.

• the same scene, its force fields allocated in two opposite orders: the assembled entry is 0 or 1 (three force fields add 1, 1e16 and -1e16 to it);
• force fields created in the reverse order of their paths are built in the order of their addresses.

MatrixSystem_sameMatrixWhateverTheAddressesOfTheComponents shows that a different ordering lead to different results

[with-all-tests]

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