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Infer.NET development : Compiler transforms

Indexing transform

Finds arrays indexed by constants or observed variables, such as a[0] or a[observedIndex], and replaces the expression with a new variable, such as a_item0. The new variable is related to the original expression through Factor.Copy. If the replaced expression was on the left hand side of an assignment, then it is assigned Factor.Copy(new variable), otherwise the new variable is assigned to Factor.Copy(original expression).

Multiple identical expressions are replaced with the same variable e.g. multiple references to a[0] are all replaced with a_item0. Only stochastic expressions are transformed.

The new declaration and the Factor.Copy must be placed in the same loop context as the array declaration. In other words, if an array is declared outside a loop but the index expression is inside, then the new statement must be placed outside.

ISSUE: what to do if expression is used on both the left and right hand side of the assignment?

Input Output
double[] x = new double[2];
bool[] b = new double[3];
for(int i=0;i<3;i++) {
b[i] = Factor.IsPositive(x[0]);
}		 double[] x = new double[2];
bool[] b = new double[3];
double x_item0 = Factor.Copy(x[0]);
for(int i=0;i<3;i++) {
b[i] = Factor.IsPositive(x_item0);
}
double[] x = new double[2];
x[0] = Factor.Gaussian(0,1);
x[1] = Factor.Gaussian(x[0],1);		 double[] x = new double[2];
double x_item0 = Factor.Gaussian(0,1);
x[0] = Factor.Copy(x_item0);
double x_item1 = Factor.Gaussian(x_item0,1);
x[1] = Factor.Copy(x_item1);