coefficients of differential equation defined by strings

I have a differential equation as string like

a*x1''[t] + b*cos(x2[t])*x1''[t] - n*x2'[t]*x1'[t]*sin(x2[t])-
c*(x2'[t])^2*sin(x2[t]) + g*cos(x1[t]) = In

and I want to extract the coefficients of

x1''[t], x1'[t], x2'[t]

and also extract the rest (which does not include any of these variables) as another term.

Is there a way to do it?

[Walter Roberson]

regexp() for analysis.

However, you have terms inside of function calls such as cos(), so it is not clear that you want to come up with a single list of coefficients: it might make more sense to have a list for each function call level.

If different mentions of a variable have different coefficients, do you want the coefficients added together, or two separate entries? If added together, then what if they are at two different call levels?

[F R]

Thanks, I want to have summed coefficients for each variable. For example the coefficients of

x1''[t]

should be summed up and returned as

(a + b*cos(x2[t]))

[Walter Roberson]

How do you want to handle the fact that you have x2'[t]^2 ? Do you want the coefficients for each power of each derivative ?

Analysis that needs to be able to handle (expression)^power and properly extract the coefficients of the variables by expansion, is not so easy to handle properly. Can we assume that the symbolic toolbox is present?

[F R]

I want to extract the coefficient of x2'[t], so it should return

-c*x2'[t]*sin(x2[t])

yes, any toolbox which can handle this in Matlab is appreciated