How change the slopes in a curve from positive to negative

We hve a set of data points representing a curve.when the y value is greater than 345, for any line between two points, if the line had a positive slope we need to flip its sign and make it negative. attached is the data we are using and an image of the part of the curve that we would like to modify

Any idea how this can be done?

[DGM]

Describe the specific conditions used to determine when a change should be made. Also, you appear to be plotting the data transposed (i.e. the inxb2 data is plotted on the y-axis). Is that the manner in which slope should be calculated?

[Malak]

Yes you are right I am plotting the transponse, and the slope should be calculated in this manner. I have modified the attached data to show the proper x and y data. The only specific condition is that when the y value is greater than 345 then we flip any straight line that has a positive slope to become having a negative one.

Answer 1

[chicken vector]

This works if you don't really care about the value on the y-axis:

load datapoints
inyb2 = -cumsum(abs(diff([0; inyb2])));
plot(inxb2,inyb2);