Graphing mathematical functions in java using applets

Question

I'm working this example in my java book, it is supposed to graph a mathematical function and it does work, but i don't understand the last two lines, can someone explain them to me? Assume that data is an array of doubles and holds function values for a certain 'range' in this case the range is -pi to pi.

The book has a comment for this little slice of code and i have an idea of what it is doing, but i would like to know exactly why we do the last two lines in this loop.

// Scale and translate data values
for (int i = 0; i < d.width; i++) {
        double value = data[i];
        double k = (value - min) / (max - min);
        data[i] = d.height * (1 - k);
    }

can someone help me out?

Feel free to accept and upvote the answer if you found it useful and it answered your question which seems to be the case! — Gigili
– Gigili, Commented Jul 15, 2012 at 11:12

Dawood ibn Kareem · Accepted Answer · 2012-07-14 05:10:01Z

2

Sure. In order to draw the graph, the y-values of the function need to be scaled, so that they fit within the height of the area in which they'll be drawn. So k is a scaled version of y that's in the range 0 to 1 - that is, the minimum value will map to 0 and the maximum value will map to 1. Lastly, find the data point to draw by converting k into a value between 0 and d.height.

answered Jul 14, 2012 at 5:10

Dawood ibn Kareem

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3 Comments

rage Over a year ago

Thank you, i don't fully understand the explanation but i will once i pore over it a bit. Is this a standard way of doing things?

Dawood ibn Kareem Over a year ago

Pretty standard, yes. Try out different values of max, min and value, to see what happens with k, and with d.height. Then you'll understand.

rage Over a year ago

ok its making more sense. I did a simple example with the numbers {1,2,3,4,5} and in order to map these numbers to 0-1 you do indeed need to do: value - min/difference between max and min. I feel like i have seen this before when dealing with Math.random() for some reason..

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