Linear Regression

[richkonar50]

Does anyone know how to use a regression equation to solve for y
without typing all of the numbers out?

[Daniel Dudley]

If I understand you correctly, you can do the regression on either the
spreadsheet or the calculator page. It will ask you in the dialog box
if where you want the output equation to be. The default, I believe is
f1. Then from the calculator page, you can you can type f1(25) (for
example) and it will put 25 into the function and tell you what y (f) is
equal to for that x. However, you cannot solve for x for some given y.
Unless, you plot a point on the graph of f and then edit the y
coordinate.

Dan

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[Andy Kemp]

If it puts the function in as f1, then

nSolve(f1(x)=25,x)

Would solve for a y value of 25...

Sent from my iPhone

[lee kucera]

Or, after you have found the line, use Stat.RegEqn(25) to find the y-value. Unlike the 84, it does not show you the actual equation you are using.
lk

Dan

lee kucera
a.p. statistics
leek...@gmail.com

[Nelson Sousa]

the coefficients are stored as stat.a and stat.b

Beware that stat. is the prefix for stats vars for the first stat
calculation; the second one will have stat1. as prefix; the third one
will be stat2. and so on.

You can see all the variables on the var menu.

You also have the functions stat.results() that display the entire set
of variables for each calculation.

Cheers,
Nelson

[tmb-Travis]

I know how to get fractions for the stat variables using Menu, Number
and then var on the calc page.
Is there a way to get fractions on the graph page?

> > leekuc...@gmail.com

[Nelson Sousa]

g&g is a inherentely numerical app, so all results are decimal and can't be displayed as fractions.

However... there's a trick.

On two text boxes write getnum(approxrational(x,10^-n)) and getdenom(approxrational(x,10^-n)), replacing n for a suitable tolerance. warning: the precision of G&G is around 5 or 6 decimal places at most, so use a low n as the tolerance. Otherwise you won't get good results.

Now calculate both formulas using the number you want to convert to fraction as x. You get both the numerator and denominator. With attach, glue the denominator below the numerator. All you need now is a text message with __ to fake a fraction. Move it to the space between the numbers.

Limitations: the two numbers will be aligned to the left. It will be ugly for things like 5/12;
If the numerator and denominator grow too much (like 101/375), you fraction won't look good as both numbers will be wider than the fraction bar;
If the fraction is negative the - sign will appear on the numerator. Again, ugly.

Going one (or several) steps further: Attach each number to an empty label of a 0 radius circle and have its appear on a position determined as a funtion of log(x);
Build several fraction bars of different widths as labels of 0 radius circles and determine their position and which one should be visile by the size of the numbers;
Use abs to isolate the sign and add is separately as an appearing/disappearing label.

These improvements are rather complex, but make fractions look really nice. However, they require a lot of expertise on the G&G app. If anybody wants to try it, email me and I'll guide you through it.

Cheers,

--
Nelson