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## [Octave-bug-tracker] [bug #49871] ode15s, MStateDependence option incorr

 From: Rik Subject: [Octave-bug-tracker] [bug #49871] ode15s, MStateDependence option incorrect Date: Tue, 4 Feb 2020 19:22:33 -0500 (EST) User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; rv:11.0) like Gecko

```Follow-up Comment #3, bug #49871 (project octave):

From
http://www.ece.northwestern.edu/local-apps/matlabhelp/techdoc/ref/ode45.html

The solvers of the ODE suite can solve problems of the form , with time- and
state-dependent mass matrix . (The ode23s solver can solve only equations with
constant mass matrices.) If a problem has a mass matrix, create a function M =
MASS(t,y) that returns the value of the mass matrix, and use odeset to set the
Mass property to @MASS. If the mass matrix is constant, the matrix should be
used as the value of the Mass property. Problems with state-dependent mass
matrices are more difficult:

If the mass matrix does not depend on the state variable and the function
MASS is to be called with one input argument, t, set the MStateDependence
property to 'none'.
If the mass matrix depends weakly on , set MStateDependence to 'weak' (the
default) and otherwise, to 'strong'. In either case, the function MASS is
called with the two arguments (t,y).

From
http://www.ece.northwestern.edu/local-apps/matlabhelp/techdoc/math_anal/diffeq7.html#688417

MStateDependence
none | {weak} | strong
Dependence of the mass matrix on . Set this property to none for
problems .
Both weak and strong indicate , but weak results in implicit solvers using
approximations when solving algebraic equations.

Maybe this helps someone who understands the code better.

It doesn't appear that this option should affect the Jacobian option which is
separate.

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<https://savannah.gnu.org/bugs/?49871>

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```