Confused about fiber section calculation

[linguan118]

Dear fmk,
When I was reading following codes in FiberSection2d.cpp
FiberSection2d::setTrialSectionDeformation (const Vector &deforms)
{
e = deforms;
double d0 = deforms(0);
double d1 = deforms(1);

for (int i = 0; i < numFibers; i++) {
double y = fiberLocs[i] - yBar;
// yBar is ∑Aiyi/∑Ai the centroid of the section

// determine material strain and set it
double strain = d0 - y*d1;
}
}

I assume that fiberLocs is defined by users.
I'm very confused about y, because y is the distance of the fiber to the centroid location instead of the neutral axis of the section. The neutral axis is not calculated here.
Thank you for your attention.

[linguan118]

Sorry I figured it out!
I wonder if d0 is the axial strain of the centroid location of the section.