============================================================ ============================================================ CHAPTER 1: SECTION 1.3.6 ROOTPLOT PAGE: 22 In[121]:= There is an error in rootPlot. As written, it will only work for the variable "x". The correction is below. rootPlot[equation_, variable_:x, opts___] := Module[{nSol, list}, nSol = NSolve[equation, variable]; list = {Re[variable], Im[variable]} /. nSol; Return[ ListPlot[list, PlotStyle -> PointSize[0.03], opts]]; ] In the above equation, the third line: list = {Re[x], Im[x]} /. nSol; is replaced by list = {Re[variable], Im[variable]} /. nSol; so the relation will work for any variable, not just "x". Thanks to Ken Caviness. ============================================================ ============================================================ CHAPTER 6: SECTION 6.2 Problem 4: Springs Mounted on Top of a Carriage PAGE: 319 In[83]:= (* Original version *) ySol=(uSol-xSol //Together)/.I->1//Simplify (* Corrected version: 20 Sept. 2006 *) ySol=(uSol-xSol //Together)/I //Simplify The original version will not work in general. Since ySol is the complex part, we can simply divide by I. Note, in general rules, replacements such as /.I->1 will not work. The more general form, such as in In[82] must be used to correctly make substitutions with complex numbers. For example; In[82]:= xSol = uSol /. Complex[a_, b_] -> Complex[a, 0] // Simplify Thanks to Hector Aceves Campos ============================================================ ============================================================ ============================================================ ============================================================ ============================================================ ============================================================ ============================================================ ============================================================