Slope and Intercept calculations in JSL

uday_guntupalli — Sat, 21 Apr 2018 12:31:01 GMT

@Jeff_Perkinson , @Milo ,
This is in reference to a discussion - Slope and intercept functions
I have found this discussion to be helpful. I am currently using JMP 13, so if there are developments made in JMP 14, I dont necessarily have access to it.

But, here are my questions:

Clear Log() ; Clear Globals(); Close All(DataTables,"No Save");  

Slope = function({x,y},{default local},
				If( !(Is Matrix( x ) & Is Matrix( y ) & N Col( x ) == 1 & N Col( y ) == 1),
					Show( "x or y arguments are not matrices or they have more than one column" );
					Throw();
					,
					x = J( N Row( x ), 1 ) || x; // put in an intercept column of 1s 
					beta = Inv( X` * X ) * X` * Y; // the least square estimates 
					beta[2];
				  );
				); 
				
Intercept = function({x,y},{default local},
					 If( !(Is Matrix( x ) & Is Matrix( y ) & N Col( x ) == 1 & N Col( y ) == 1),
						Show( "x or y arguments are not matrices or they have more than one column" );
						Throw();
						,
						x = J( N Row( x ), 1 ) || x; // put in an intercept column of 1s 
						beta = Inv( X` * X ) * X` * Y; // the least square estimates 
						beta[1];
					   );
					); // end of intercept function 

x1 = 0.05417099; 
x2 = 0.057730865; 
y1 = 30.5885; 
y2 = 31.5885; 

dt = New Table(); 
dt << New Column("X",Numeric,Continuous,<< Set Values({x1,x2}))
   << New Column("Y",Numeric,Continuous,<< Set Values({y1,y2}));
   
dt << New Script("Biv",Bivariate( Y( :Y ), X( :X ), Fit Line( {Line Color( {213, 72, 87} )} ) ));
 
SlopeTest = Slope(Matrix({y1,y2}),Matrix({x1,x2})); 
Show(SlopeTest);
InterceptTest = Intercept(Matrix({y1,y2}),Matrix({x1,x2})); 
Show(InterceptTest);

1. Why do the slope and intercept not match for the test case that I have taken w.r.t bivariate ?

2. If the function or its implementation have a bug, would you be kind enough to offer an alternative ?

Re: Slope and Intercept calculations in JSL

cwillden — Fri, 20 Apr 2018 18:30:29 GMT

You got the arguments backward for the Slope and Intercept function. Just reverse the order of the matrices.

Re: Slope and Intercept calculations in JSL

uday_guntupalli — Fri, 20 Apr 2018 18:35:55 GMT

@cwillden,
While that was a good catch, that did not change the results and the function doesn't match up to bivariate

Re: Slope and Intercept calculations in JSL

cwillden — Fri, 20 Apr 2018 18:59:51 GMT

Hey @uday_guntupalli,

You still got the arguments reversed. See the screenshot:

Re: Slope and Intercept calculations in JSL

vince_faller — Fri, 20 Apr 2018 19:00:37 GMT

The order of your inputs are backwards. On the function it goes slope(x, y) and when you call you're doing slope(y, x)

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Slope and Intercept calculations in JSL

Re: Slope and Intercept calculations in JSL

Re: Slope and Intercept calculations in JSL

Re: Slope and Intercept calculations in JSL

Re: Slope and Intercept calculations in JSL