diff --git a/java/src/org/broadinstitute/sting/playground/gatk/walkers/genotyper/ExactAFCalculationModel.java b/java/src/org/broadinstitute/sting/playground/gatk/walkers/genotyper/ExactAFCalculationModel.java
index 99007e626..a347ab8a7 100755
--- a/java/src/org/broadinstitute/sting/playground/gatk/walkers/genotyper/ExactAFCalculationModel.java
+++ b/java/src/org/broadinstitute/sting/playground/gatk/walkers/genotyper/ExactAFCalculationModel.java
@@ -26,6 +26,7 @@
 package org.broadinstitute.sting.playground.gatk.walkers.genotyper;
 
 import org.apache.log4j.Logger;
+import org.broadinstitute.sting.utils.*;
 import org.broadinstitute.sting.gatk.contexts.ReferenceContext;
 import org.broadinstitute.sting.gatk.refdata.RefMetaDataTracker;
 
@@ -34,6 +35,10 @@ import java.io.PrintStream;
 
 public class ExactAFCalculationModel extends AlleleFrequencyCalculationModel {
 
+    private int maxNumIterations = 50;
+    private double tol = 1e-4;
+    private boolean DEBUGOUT = true;
+
     protected ExactAFCalculationModel(int N, Logger logger, PrintStream verboseWriter) {
         super(N, logger, verboseWriter);
     }
@@ -44,7 +49,90 @@ public class ExactAFCalculationModel extends AlleleFrequencyCalculationModel {
                                 double[] log10AlleleFrequencyPriors,
                                 double[] log10AlleleFrequencyPosteriors) {
 
-        // TODO: implement me based on
+        // Math requires linear math to make efficient updates.
+        double[] alleleFrequencyPosteriors = MathUtils.normalizeFromLog10(log10AlleleFrequencyPriors);
+
+        // now that we have genotype likelihoods for each sample, we can start refining allele frequency estimate
+        double meanAF = computeMeanAF(alleleFrequencyPosteriors);
+        if (DEBUGOUT)
+            System.out.format("Initial Mean AF: %5.6f\n", meanAF);
+
+
+        for (int numIterations=0; numIterations < maxNumIterations; numIterations++) {
+            double oldMeanAF = meanAF;
+            alleleFrequencyPosteriors = updateAFEstimate(GLs, alleleFrequencyPosteriors);
+            meanAF = computeMeanAF(alleleFrequencyPosteriors);
+
+            if (DEBUGOUT)
+                System.out.format("Mean AF: %5.4f. PVariant: %5.5f\n", meanAF,1.0-alleleFrequencyPosteriors[0]);
+
+            if (Math.abs(meanAF-oldMeanAF) < tol)
+                break;
+
+        }
+
+        for (int k=0; k < alleleFrequencyPosteriors.length; k++)
+            log10AlleleFrequencyPosteriors[k] = Math.log10(alleleFrequencyPosteriors[k]);
 
     }
+
+    private double[] updateAFEstimate(Map<String, BiallelicGenotypeLikelihoods> GLs, double[] alleleFrequencyPriors) {
+
+        int numSamples = GLs.size();
+        int numChr = 2*numSamples;
+
+        double[][] YMatrix = new double[1+numSamples][1+numChr];
+        YMatrix[0][0] = 1.0;
+        int j=0;
+
+        for ( String sample : GLs.keySet() ) {
+            j++;
+
+            double[] genotypeLikelihoods = MathUtils.normalizeFromLog10(GLs.get(sample).getLikelihoods());
+            double sum = 0.0;
+            double den = 2.0*j*(2.0*j-1);
+
+            for (int k=0; k <= 2*j; k++ ) {
+                double tmp = (2.0*j-k)*(2.0*j-k-1)*YMatrix[j-1][k] * genotypeLikelihoods[2];
+                if (k > 0)
+                    tmp += (2.0*k)*(2.0*j-k)*YMatrix[j-1][k-1]*genotypeLikelihoods[1];
+                if (k > 1)
+                    tmp += k*(k-1)*YMatrix[j-1][k-2]*genotypeLikelihoods[0];
+
+                YMatrix[j][k] = tmp/den;
+
+                sum += YMatrix[j][k];
+            }
+            // renormalize row
+            for (int k=0; k <= 2*j; k++ )
+                YMatrix[j][k] /= sum;
+
+        }
+        double sum = 0.0;
+        double[] newAF = new double[alleleFrequencyPriors.length];
+
+        for (int k=0; k <= numChr; k++) {
+            double prod = YMatrix[j][numChr-k] * alleleFrequencyPriors[k];
+            newAF[k] = prod;
+            sum += prod;
+        }
+        //renormalize now
+        for (int k=0; k < newAF.length; k++)
+            newAF[k] /= sum;
+
+        return newAF;
+
+
+    }
+
+    private double computeMeanAF(double[] afVector) {
+        // get now new site AF estimate
+        double sum = 0.0;
+        for (int k=0; k < afVector.length; k++)
+            sum += (double)k * afVector[k];
+
+        return  sum/afVector.length;
+
+    }
+
 }
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