Seite - 66 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Band Second Edition

66 3 LoopsandBranching Fig. 3.1 Vertical position ofball The loop will run as long as the conditiony[i] >= 0 evaluates toTrue. Note that the programmer introduced a variable by the name i, initialized it (i = 0) beforetheloop,andupdatedit (i = i + 1) in theloop.So,eachtimethecondition y[i] >= 0 evaluates to True, i is explicitly increased by 1, allowing a check of successiveelements in thearrayy. Whentheconditiony[i] >= 0evaluatestoFalse,programexecutionproceeds with thecodelinesafter the loop.Thismeansthat, afterskippingthecomments, the timeofflight isprinted,followedbyaplottingof theheights(toallowaneasycheck of the timeofflight). Reporting the Answer Remember that the height is computed at chosen points in time only, so, most likely, we do not have the time for when the height is exactlyzero.Thus,reportingt[i]asthetimeofflight isanapproximation.Another alternative,couldbetoreport0.5*(t[i-1] + t[i])as theanswer,reasoningthat sincey[i] isnegative(which is whythe loop terminated),t[i]mustbe too large. Runningthe Program Ifyou run thisprogram,youget theprintout Time of flight (in seconds): 0.917918 and the plot seen in Fig.3.1. The printed time of flight seems consistent with what wecan readoff fromthe plot. 3.2.2 CharacteristicsofaTypicalwhileLoop LoopStructureandInterpretation Thestructureofa typicalwhile loopmaybe putupas while some_condition: # Loop header <code line 1> # 1st line in loop body