Short Mathematica Example for Numerical Methods
Lecturer: Dr. Rennan Barkana

When you use NDSolve[] in Mathematica, the resulting solution is not
stored as a function. Rather, it is a kind of rule for finding the
solution function. To use this rule, you have to use the Evaluate[]
function, and specify the rule. So below, we call the solution rule t,
and then we evaluate the function y[x] under this rule. The
Mathematica notation for specifying a rule is /.
Note a difference between Plot[] and ParametricPlot[]. When we Plot[]
two functions, each function is plotted separately, so we write
separate Evaluate[] calls. But ParametricPlot[] uses the same function
twice, once for the x-value and once for the y-value of the plotted
point, so there is just one Evaluate[] call around the pair of points.