/// <inheritdoc/>
public Matrix GetDMatrixAt(Element targetElement, params double[] isoCoords)
{
var elm = targetElement as BarElement;
if (elm == null)
{
throw new Exception();
}
var xi = isoCoords[0];
var geo = elm.Section.GetCrossSectionPropertiesAt(xi);
var mech = elm.Material.GetMaterialPropertiesAt(xi);
var buf =
//new Matrix(1, 1);
targetElement.MatrixPool.Allocate(1, 1);
ThrowUtil.ThrowIf(!CalcUtil.IsIsotropicMaterial(mech), "anistropic material not impolemented yet");
var g = mech.Ex / (2 * (1 + mech.NuXy));
buf.FillRow(0, geo.J * g);
return(buf);
}