From 35435019b6f73134ae59bd894c3d64395404ac4b Mon Sep 17 00:00:00 2001
From: Alex Linden Levy <alevy@mobitv.com>
Date: Tue, 27 Aug 2013 11:15:16 -0600
Subject: [PATCH] added eExpReg: uses a*e^(x*b) form of exponential and lnReg:
 logarithmic form a + b*ln(a)

---
 lib/stats.js | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 93 insertions(+), 2 deletions(-)

diff --git a/lib/stats.js b/lib/stats.js
index c875a34..6b4dead 100644
--- a/lib/stats.js
+++ b/lib/stats.js
@@ -361,10 +361,100 @@
 			};
 		},
 
-		// Calculates the exponential regression line for the data set.
+	    // A true exponential form -- lindenle@gmail.com
+	    // y = a* e ^ bx
+	    // ln y = ln a + ln e^ bx
+	    // ln y = ln a + bx
+	    
+	    // y' = ln y
+	    // m' = b
+	    // b' = ln a
+	    
+	    // y' = b' + m'x
+	    
+	    eExpReg: function() {
+		// Get y coordinates
+		var yCoords = this.pluck('y');
+		
+		
+		// Do a semi-log transformation of the coordinates
+		// y' = ln y 
+		yCoords.map(function(num) {
+		    return Math.log(num);
+		});
+		
+		// Get a new stats object to work with that has the transformed data
+		var nums = this.clone().map(function(coord, index) {
+		    return {
+			x: coord.x,
+			y: yCoords.get(index)
+		    };
+		});
+		
+		// Calculate the linear regression for the linearized data
+		var linReg = nums.linReg();
+		
+		// Calculate the coefficient for the exponential equation
+		// a = e ^ b'
+		var coefficient = Math.pow(Math.E, linReg.yIntercept);
+		
+		// Calculate the base for the exponential equation
+		// b = m'
+		var weight = linReg.slope;
+		
+		return {
+		    coefficient: coefficient,
+		    weight: weight,
+		    r: linReg.r
+		};
+	    },
+	    //-------------
+	    // Logarithmic
+	    //--------------
+	    // y = a + b ln x
+	    // x' = ln(x)
+	    // y = a+bx' 
+	    lnReg: function() {
+		// Get y coordinates
+		var xCoords = this.pluck('x');
+		
+		
+		// Do a semi-log transformation of the coordinates
+		// x' = ln x 
+		xCoords.map(function(num) {
+		    return Math.log(num);
+		});
+		
+		// Get a new stats object to work with that has the transformed data
+		var nums = this.clone().map(function(coord, index) {
+		    return {
+			x: xCoords.get(index),
+			y: coord.y
+		    };
+		});
+		
+		// Calculate the linear regression for the linearized data
+		var linReg = nums.linReg();
+		
+		// Calculate the coefficient for the exponential equation
+		// a = e ^ b'
+		var coefficient = linReg.slope;
+		
+		// Calculate the base for the exponential equation
+		// b = m'
+		var offset = linReg.yIntercept;
+		
+		return {
+		    coefficient: coefficient,
+		    offset: offset,
+		    r: linReg.r
+		};
+	    },	
+	        // Calculates the exponential regression line for the data set.
 		//
 		// Returns an object with the coefficient, base, and correlation
 		// coefficient for the linearized data.
+
 		expReg: function() {
 			// Get y coordinates
 			var yCoords = this.pluck('y');
@@ -398,6 +488,7 @@
 			};
 		},
 
+	    
 		// Calculates the power regression line for the data set.
 		//
 		// Returns an object with the coefficient, base, and correlation
@@ -941,4 +1032,4 @@
 		// Just write to window (or whatever is the root object)
 		root.stats = stats;
 	}
-}(this));
\ No newline at end of file
+}(this));