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Locus

Another exclusive Foundation RISCWorld application

Exercise 8. Fitting curves

Another use which can be made of data sets is in curve fitting. Let us suppose that you are studying cubic graphs and the principle of dominance. The teacher could set up a data set file with points from the graph of y=x�-3x�+x-4 (such a file is supplied in the DataSets folder which comes with the application: it is called Cubic.)

Make sure that Auto-Scaling is switched on and drag the file to the main Locus window. Locus will scale the axes appropriately and a series of points will be plotted.

The student could now try out different functions to see whether they fit the points.

A first guess might be y=x� which could be plotted in the usual way. Obviously this does not fit so a second guess might be y=x�-4 which would show that the student has understood the idea of the constant value in the equation corresponding to the y-intercept.

By altering the formula in a methodical way the student should eventually come up with the correct formula. Of course this is a fairly complicated example and this facility can be used at a much lower level: for example to fit the graph of y=x+2.

You can plot the graphs with auto-scaling switched on or off, though the main window will become a bit messy after a while if it is off.

Of course it perfectly possible to press the clear button and then reload the data set file though it would be a nuisance to have to do this. So to alleviate this problem you should click on the clear button with ADJUST (the right hand mouse button) and this will remove the graphs without deleting the data set.

Foundation RISCWorld