Seite - 20 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python

20 1 TheFirstFewSteps Thenyoucould (inprinciple)doa lot ofother things inyourcode,beforeyouplot thesecondcurveby plt.plot(family_member_no, H) plt.hold(’off’) Notice the use ofhold here. hold(’on’) tells Python to plot also the following curve(s) in the samewindow. Python does so until it readshold(’off’). If you donotuse thehold(’on’)orhold(’off’)command, the secondplot command will overwrite thefirstone, i.e., yougetonly the secondcurve. In case youwould like the two curvesplotted in two separate plots, youcando thisbyplotting thefirst curvestraightforwardlywith plt.plot(family_member_no, h) thendoother things inyourcode,beforeyoudo plt.figure() plt.plot(family_member_no, H) Note how the graphs are made continuous by Python, drawing straight lines be- tween the fourdata points of each family. This is the standardwayofdoing it and wasalsodonewhenplottingour1001heightcomputationswithball_plot.py in Chapter1.4.However, since therewere somanydatapoints then, thecurve looked niceandsmooth. Ifpreferred,onemayalsoplotonly thedatapoints. For example, writing plt.plot(h, ’*’) willmarkonly thedatapointswith the star symbol.Other symbols like circles etc. maybeusedaswell. There aremany possibilities in Python for adding information to a plot or for changing its appearance. For example,youmayadda legendby the instruction plt.legend(’This is some legend’) oryoumayadda title by plt.title(’This is some title’) Thecommand plt.axis([xmin, xmax, ymin, ymax]) will define the plotting range for the x axis to stretch from xmin to xmax and, similarly, theplotting range for they axis fromymin toymax. Saving thefigure to file is achievedby thecommand