Wednesday, April 3, 2013

plotting an equation in excel

For plotting equation we need X and Y, thus Y is function of X.

We need two things to specify:

(1) Bin of estimate - if bin of estimate is low will produce nice and smoother line.

(1) X and Y limit, this depends upon the equations and the portion of the curve you want to see.


X^2 *Y^2 =1

By solving the quation, we get:

X = (1/Y^2)^-2

Please note operators in Excel:

Subtraction - minus sign ( - )
Addition - plus sign ( + )
Division - forward slash ( / )
Multiplication - asterisk (* )
Exponentiation - caret (^ )

Also order of operation is  Brackets, Exponents, Division, Multiplication, Addition, Subtraction.

Let's calculate values creating formula in Excel:

The formula for the first cell becomes:


Here the bin is set to 0.1 and range of X values from -4 to -4.

Data series ready, just plot scatter plot with smoothed line:

We can add other formulas to the plot, just by adding the series. To do so we need to repeate calculation at certain bin interval.

Plotting a circle:
(x-4)2 + (y-2)2 = 25

We need to plot two equations:

Between range of -1 to 9, create X bins and calculate the values.

Similarly we can plot any equation or density functions.

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