Adding Forward Euler in Java #387
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Gathros
added
the
Implementation
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Hey @CDsigma I think you know, but we are missing some Java expertise, so I don't know who will review this. I'll do so if no one steps up. |
| public static void main(String[] args) { | ||
| double timeStep = 0.01; | ||
| int n = 100; | ||
| double threshold = 0.01; |
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You can make these variables as memebers of the class so that all methods can access them without needing to pass them as arguments
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I disagree. These should be passed as arguments.
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Alright. I'll go ahead and review this one. I'm not the most proficient person in Java out there, but it'll do.
First of all, your indentation is all over the place. We use 4 spaces in the AAA, but you used 2. Some lines with closing braces (12, 36) are not indented at all, even though they should be. Please fix that.
Secondly, your class (ForwardEuler) does not have the same name as the file it's in (Euler.java). I suggest you rename the file to ForwardEuler.java.
| boolean isApprox = checkResult(result, threshold, timeStep); | ||
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| if(isApprox) { | ||
| System.out.print("All values within threshold"); |
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Please use System.out.println here or otherwise add a newline to the output. I assume you're using Windows, so everything works as expected, but when I run this on Linux, my shell does this:
user@hostname:aaa> java ForwardEuler
All values within thresholduser@hostname:aaa>
instead of this:
user@hostname:aaa> java ForwardEuler
All values within threshold
user@hostname:aaa>
| double solution = Math.pow(Math.E, -3 * i * timeStep); | ||
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| if(Math.abs(result[i] - solution) > threshold) { | ||
| isApprox = false; |
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You're missing a println before inside this block. If you look at the reference implementation (Julia), you'll see this:
if (abs(euler_result[i] - solution) > threshold)
println(euler_result[i], solution)
is_approx = false
end| double[] result = {1}; | ||
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| for(int i = 0; i < n; i++) { | ||
| result = append(result, result[i] - 3 * result[i] * timeStep); |
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You're thinking way too complicated here. You could just make result an array with a length of n (double[] result = new double[n]), add the initial value of 1 (result[0] = 1) and then fill the array like this:
result[i] = result[i - 1] - 3 * result[i - 1] * timeStep;The loop would of course have to start from 1 to skip the first element.
This way, you could drop the append method above. In addition to that, if I'd need an append method for an array, I'd use an ArrayList instead.
| boolean isApprox = true; | ||
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| for(int i = 0; i < result.length; i++) { | ||
| double solution = Math.pow(Math.E, -3 * i * timeStep); |
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There's a method Math.exp(double a) which does exactly this.
double solution = Math.exp(-3 * i * timeStep);
| @@ -121,6 +121,8 @@ Full code for the visualization follows: | |||
| [import, lang:"matlab"](code/matlab/euler.m) | |||
| {% sample lang="swift" %} | |||
| [import, lang:"swift"](code/swift/euler.swift) | |||
| {% sample lang="java" %} | |||
| [import, lang:"java"](code/java/Euler.java) | |||
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Don't forget to update the file name in case you rename the source file.
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This PR has been stale for over 10 days now and you haven't shown up in Discord either. I'm assuming you're on a vacation or you're preoccupied by something else. Either way, we have another PR for Forward Euler in Java in #518, so I'm going to go ahead and work with that one. I'm sure you'll understand. |
Added Forward Euler in Java