DPlot

Is there any option for piecewise linear fitting of 7 line segments through an earthquake response spectrum in a tripartite grid using least square fitting method and to get the break points of the fitted curve ??
There is few constraints :
1.) The third line segment should have a slope of 45 degrees (ie. parallel to the acceleration lines in atripartite grid)
2.) Slope of fourth line segment should be zero (horizontal)
3.) slope of the fifth line segment should be -45 degrees ( parallel to the displacement lines of the tripartite grid)

Controlling slope and/or magnitude can be done with Generate>More Curve Fits and fixing the appropriate coefficients. For example for your third line segment you'd enter -1 for B and check the Hold box.

There's no way to do this for 7 line segments at once, though.