Seite - 5 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python

1.2 APythonProgramwithVariables 5 the sign # it takes the rest of the line as a comment. Python then simply skips reading the rest of the line and jumps to thenext line. In the code, you see several suchcomments andprobably realize that theymake it easier for you tounderstand (orguess)what ismeantwith thecode. Insimplecases, commentsareprobablynot muchneeded,butwill soonbe justifiedas the levelofcomplexity stepsup. Thenext line readbyPython is v0 = 5 # Initial velocity In Python, a statement likev0 = 5 is knownas anassignment statement (very differentfromamathematicalequation!). Theresultontheright-handside,herethe integer5,becomesanobjectandthevariablenameonthe left-handside isanamed referenceforthatobject.Wheneverwewritev0,Pythonwill replaceitbyaninteger with value5. Doingv1 = v0 creates a newname,v1, for the same integer object withvalue5andnot acopyofan integerobjectwithvalue5. Thenext two lines g = 9.81 # Acceleration of gravity t = 0.6 # Time areof thesamekind, sohavingread themtoo,Pythonknowsof threevariables (v0, g, t) and their values. These variables are then used byPythonwhen it reads the next line, theactual “formula”, y = v0*t - 0.5*g*t**2 # Vertical position Again, according to its rules, Python interprets* asmultiplication,- asminus and ** as exponent (let us also add here that, not surprisingly, + and /would have been understood as addition and division, if such signs had been present in the expression). Having read the line, Python performs themathematics on the right- handside,andthenassignstheresult (inthiscasethenumber1.2342)tothevariable namey. Finally,Pythonreads print y This makes Python print the value of y out in that window on the screen where youstarted theprogram.Whenball.py is run, thenumber1.2342appearson the screen. In the codeabove,yousee severalblank lines too. Theseare simply skippedby Python andyoumayuse asmanyas youwant tomake anice and readable layout of thecode. 1.2.3 WhyNotJustUseaPocketCalculator? Certainly,finding theanswerasdoneby theprogramabovecouldeasilyhavebeen donewith a pocket calculator. No objections to that and no programmingwould havebeenneeded.However,what if youwould like tohave thepositionof theball