Calculating Derivatives/Slopes in JMP

natalie_

Hello again,

I have to columns of data, let's call them x and y.  I want to calculate the center derivative of y with respect to x (dy/dx).  If I am using the center derivative, that means I will be "missing" a point at the beginning and end of the dy/dx column.

For example, in row two of dy/dx, I want it to equal dy/dx = y3-y1/x3-x1 and on row three of dy/dx, I want it to equal dy/dx = y4-y2/x4-x2.  I am having a hard time not using jmp like I would with excel, so I am not even sure if is possible to do this in the formula editor.

Thanks!

pmroz

This code should give you some ideas.  The column formula makes use of the LAG function:

dt = open("$sample_data\Big Class.jmp");

// Create formula column

// Height = X

// Weight = Y

// dy/dx = (y+1) - (y-1)/(x+1) - (x-1)

// y+1: lag(:weight, -1)

// y-1: lag(:weight, 1)

// x+1: lag(:height, -1)

// x-1: lag(:height, 1)

dt << New Column( "dy/dx",

            Numeric,

            Continuous,

            Format( "Best", 12 ),

            Formula( lag(:weight, -1) - lag(:weight, 1) / lag(:height, -1) - lag(:height, 1))

      );