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So this is my code for Euler's method to approximate ode's. f_ being the ode, t0_ the start of the interval, tf_ the end, y0_ initial condition, h_ the step size, and y_ is a given exact solution.

euler[f_, t0_, y0_, tf_, h_, y_] := Module[{},  
 t[0] = t0;  
 w[0] = y0;  
 n = Rationalize[(tf - t0)/h];  
Do[  
  w[i] = w[i - 1] + h*f[t[i - 1], w[i - 1]];  
  t[i] = t[i - 1] + h,  
  {i, 1, n}];  
Print["Euler's Method Results:"];  
TableForm[  
Table[{i, t[i], w[i], y[t[i]], Abs[w[i] - y[t[i]]]}, {i, 0, n}],   
TableHeadings -> {None, {"i", "ti",  
   "Euler's \nMethod \nwi","Exact \nSolution\ny(ti)",  
   "Absolute \nError \n|wi-y(ti)|\n"}},  
TableAlignments -> Center, TableSpacing -> {2, 5}  
]  
]

The code works fine so I'm not worried about that, but I can't figure out how to plot the Euler's method solution. I expect it to be something like 

Plot[w[i], {i, 0, n}, PlotLabel -> "Exact solution",AxesLabel -> {"t", "y"}]

but I can't seem to make it work.

J. M.'s missing motivation
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JakeRyan34
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  • Have you seen this? – J. M.'s missing motivation Apr 09 '18 at 13:28
  • Yeah I was just looking at that and I will admit I do not understand it. I'm not really a cs person, just a math student who got pulled into a mathematica class. My professor walked us through the code that I have, but we ran out of time before she showed us how to plot it. – JakeRyan34 Apr 09 '18 at 13:31
  • Well, I'm not a "CS person" either. ;) Anyway: so you wrote this implementation of Euler's method yourself, or is this adapted from your prof's implementation? – J. M.'s missing motivation Apr 09 '18 at 13:33
  • Yeah it's adapted from hers. She pretty much gives everyone the code for an example and then changes the question a little bit on the homework. I guess so everyone does it in a similar way – JakeRyan34 Apr 09 '18 at 13:36
  • So looking at that question, if i make a table with my ti and wi pairs, can i use that ListLinePlot command to plot it? – JakeRyan34 Apr 09 '18 at 13:37
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    I had asked because the programming style really isn't something I can endorse, but this isn't a good time to give your prof surprises. Anyway, try this: euler[f_, t0_, y0_, tf_, h_] := Module[{n, t, w}, t[0] = t0; w[0] = y0; n = Rationalize[(tf - t0)/h]; Do[w[i] = w[i - 1] + h f[t[i - 1], w[i - 1]]; t[i] = t[i - 1] + h, {i, 1, n}]; ListLinePlot[Table[t[i], w[i], {i, 0, n}]]]. – J. M.'s missing motivation Apr 09 '18 at 13:40
  • Hmm doesn't seem to be working. – JakeRyan34 Apr 09 '18 at 13:47
  • Table::iterb: Iterator {w[i]} does not have appropriate bounds. It's giving me several of these error messages – JakeRyan34 Apr 09 '18 at 13:49
  • Also, when i try to add something to the module a little grey x pops up next to it. Any idea what that's about? I couldn't find any mention of it on google or anything – JakeRyan34 Apr 09 '18 at 13:50
  • Uff, sorry; that'll teach me to code while cooking dinner. Try this: eulerPlot[f_, t0_, y0_, tf_, h_] := Module[{n, t, w}, t[0] = t0; w[0] = y0; n = Rationalize[(tf - t0)/h]; Do[w[i] = w[i - 1] + h f[t[i - 1], w[i - 1]]; t[i] = t[i - 1] + h, {i, 1, n}]; ListLinePlot[Table[{t[i], w[i]}, {i, 0, n}]]]. As for that tiny multiplication sign, see this. – J. M.'s missing motivation Apr 09 '18 at 14:08
  • Had to put ListLine in a print command but it looks like that works! Thanks for the help – JakeRyan34 Apr 09 '18 at 14:12

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