I've been trying to get lsode to work on a second order ODE by breaking it into two firsts, but can't seem to figure out the syntax. Does anyone have a code example I could look at? x'(t)=y(t) y'(t)=rx(t) I was able to code it and get it to plot using a for loop, but I'd really like to see how it could be done with lsode. Thanks, Chris