Showing Revision 4 created 05/25/2016 by Udacity Robot.

1. Title:
   Arithmetic Operations 2 - Intro to Java Programming
2. Description:

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   Initially, if I compile and run the tester, all
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   of the methods are actually returning zeros. Let's fix
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   the amdahl Speedup first. Right now, it's returning 0.
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   What if I just write it in sort of the
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   way it is? Now, if I run the tester
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   again, I'm getting an actual of 2.875. When I
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   expected 1.6. I think I'd better go back and
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    fix it. Right now, this is doing the divisions first,
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    so 1 over s, and s over n.
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    And then the additions and subtractions in the middle.
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    And there's no real sense of the fraction
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    that we started with. This whole piece From s
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    to n should stay together in the denominator,
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    and the 1 minus s needs to stay together
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    in its numerator. Let's try this again. Alright, looks
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    like Amdalh/s speed up is working, but we still
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    need to do the cross ratio. I'll try
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    doing this sort of naively again. I've written this
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    as it looks but flattened it onto one line.
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    So, if I return this quantity and I compile
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    I'm getting an error, unexpected type, required class found
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    value. This error probably doesn't make a whole lot
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    of sense to yet but this is a little
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    hint of what's to come. A pair of parentheses
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    like this immediately followed by some other quantity has another meaning.
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    In particular, if you put a type in here instead of
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    an expression like a minus c. What I need to indicate
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    is that I want to multiply, and I'll need to do it
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    over here as well. And now if I try to run
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    the tester again I'm definitely not getting right answers for the cross
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    ratio. This is because when we have a bunch of operators
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    with the same precedents Travel will just start from the left and
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    move to the right so instead of computing a
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    minus c times b minus d over in parentheses b
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    minus c times a minus d. This will do a minus c times b minus d divided by b
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    minus c and multiply that entire quantity by a
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    minus d. What I need to do here, is group
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    the denominator. I could also group the numerator, if
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    I really wanted to but it wouldn't make much of
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    a difference. If I compile again, and run the tester, I've
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    now got two methods working right. Now for the average. I might try retuning
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    the sum of all of these, all divided by four. Let's
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    see how this works. If I run the tester, it looks like it works in one case, but
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    not in the other. Let's look at the second
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    case. I'm going to go read inside of the tester.
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    The case that isn't working is when we try
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    to take the average of 3, 4, 3, and 3.
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    We should, in fact, expect 3.25, but it looks
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    like we're losing the decimal. Java is interpreting this as
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    integer division, because 4 is an integer, and a,
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    b, c and d are all declared as integers. There
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    are a few ways I could fix this. I could write 4 as 4., or 4.0 And then it would
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    get the right answer here. Or I could actually change
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    all of these ints to doubles, and then I wouldn't actually
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    need to specify that the 4 was a double. I
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    can compile this and run the tester, and it still works.
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    That's because if any of these variables are a double,
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    this whole expression in parentheses is going to come out as a
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    double, and a double divided by an int doesn't need
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    to be done with integer division, that calls for regular division.
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    This is a really easy thing to mix up. It
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    looks right to us, but the computer's going to read
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    it wrong and the compiler won't warn you. When we
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    ran this with all ints and no doubles we saw that
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    it ended up being a run time error. This is
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    a good example of why it's helpful to think about what
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    you want your answer to be beforehand. Calculate a couple
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    examples and then write your code. Good book on this quiz.