From the documentation: ```julia julia> parse_sxmath("x' == x & v' == -0.75*v") 2-element Array{Expr,1}: :(x' = x) :(v' = -0.75v) ``` Assume that the variable is called `e1`. You get `:(v' = -0.75e1)`, which is then interpreted as `-7.5` in later stages. The problem is with the `parse` call in the last line: ```julia julia> parse("v' == -0.75*v") :(v' == -0.75v) ``` This occurs in the Platooning model.