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# View of /branches/pure-cfg/test/tracto.diderot

Sat Nov 13 16:02:07 2010 UTC (10 years, 10 months ago) by jhr
File size: 2267 byte(s)
```  Creating a branch to explore a pure CFG IL
```
```// tracto.diderot
//
// simple tractography; this only traces half the path, depending on
// seedSign; caller will half to piece these together into single path
// uses midpoint method (RK2) for integration
//

input string dataFile;          // name of dataset
input real stepSz;              // size of steps
input real CLmin;               // minimum value of CL anisotropy measure
input int stepNumMax;           // max number of steps allowed, or zero if no limit

//field#1(3)[3,3] F = img ⊛ bspln3;
field#2(3)[3,3] F = img ⊛ bspln3;

actor Tracto (vec3 seedPoint, int seedSign)  // seedSign == +1 or -1
{
int         stepNum = 0;
vec3        pos = seedPoint;
//// principleEvec : tensor[3,3] -> vec3
//// * : real x vec3 -> vec3
vec3        guide = real(seedSign) * principleEvec(F@seedPoint);
real        aniso = 0.0;

update
{
if (inside (pos,F)) {
//// @ : field x vec -> tensor[3,3]
tensor[3,3] ten = F@pos;
//// CL : tensor[3,3] -> real
aniso = CL(ten);  // "CL" is a linear anisotropy measure
//// < : real x real -> bool
if (aniso < CLmin) {
// terminate because anisotropy went too low
stabilize;
}
// else
vec3 evec = principleEvec(ten);
//// dot : vec3 x vec3 -> real
//// - : vec3 -> vec3
if (dot(evec, guide) < 0.0) { evec = -evec; } // fix eigenvector sign
//// * : real x real -> real
//// * : real x vec3 -> vec3
//// + : vec3 x vec3 -> vec3
evec = principleEvec(F @ (pos + 0.5*stepSz*evec));
if (dot(evec, guide) < 0.0) { evec = -evec; } // fix eigenvector sign
guide = evec;
pos = pos + stepSz*evec;
//// + : int x int -> int
stepNum = 1 + stepNum;
//// > : real x real -> bool
//// && : bool x bool -> bool
if (stepNumMax > 0 && stepNum > stepNumMax) {
// terminate because we took too many steps
stabilize;
}
} else {
// terminate because we went out of bounds
stabilize;
}
}

}
```