I am using Mathematica and I want my for loop to produce tht[1]=tht[[1]][t], tht[2]=tht[[2]][t], ... and so on. but i keep getting an error partd: th[[1]] is greater than the depth. Does anyone know a quick fix to this? My code is below. Thanks. Clear n=4; xt=x[t]; yt=y[t]; dxt=D[xt,t]; dyt=D[yt,t]; For[c=2,c<=n+1, tht[c-1] =th[[c-1]][t]; dtht[c-1]=D[tht[c-1],t]; ++c] phit=phi[t];