What is the mass matrix in ode solvers in MATLAB?
<p>Without using a mass matrix, ode solvers like <code>ode45</code> can solve y'=f(t,y).</p>

<p>But there is an option of mass matrix in ode solvers for problems that involve a "mass" matrix, M(t,y)y'=f(t,y).</p>

<p>What exactly is the "mass" matrix? Does this term come from the mass of mass-spring system oscillation? I cannot find an example code about this in the documentation. Also, it seems that I can encode information about t and y in f(t,y) in the equation of y'=f(t,y). In what situation/example will M(t,y)y'=f(t,y) arise where M(t,y) is needed?</p>