Iam basically trying to fit a curve similar to that shown in fig (a) with 7 straight line segments (ie. 6 knots) as shown in fig (b) and I need to get the optimum knot positions. This is a tripartite plot in which there are 4 axes (vertical , one inclined at 45 degrees with horizontal, other inclined at 135 degrees with the horizontal ) and the horizontal axis and all are in log scale. Constraints are 3 rd line should be parallel to 45 degree lines, 4 th line should be parallel to the horizontal, 5th line should be parallel to 135 degree lines as shown in the attachment. – Aiswarya 11 mins ago .