1. The problem statement, all variables and given/known data I am very confused over how matlab knows which variables are changeable variables in ode45. 2. Relevant equations // 3. The attempt at a solution My input is p Earlier have defined; a = 1; k = 1; w = 1/3; Then I want to figure out adot and adoubledot from these. adot = (a)*(p - k/a)^(-1/2); adoubledot = (a/2)*(p + 3*w*p); Suddenly realised that I have no idea why matlab would let "a" change but not let "p" and "k" change... Is there a way to tell matlab that one of the variables is changing in time and the others aren't?