Finding a specific value after analysing the trend of different plots

Any suggestion how to automatize the extraction of a specific value from the X ordinates (Frequency) after analysing the trend of specific curve plots. For example, a frequency of 0.3Hz should be chosen as a representative value from the three curves because the noise does not influence on the energy and the variation has a specific trend after this value as it is shown.

Answer 1

[KSSV]

Read about interp1. You can use this to extract the values you want.

Let (x,y) be your data and you want yi for xi:

yi = interp1(x,y,xi) ;

[Jorge Luis Paredes Estacio]

Thanks for the answer. But, in this case I want to generate a script to detect automatically the value of the X ordinates (one frequency value) and this should be done when the variation of the three curves is analysed. As you can see in this example plot from one signal, the noise still affects the energy variation on the three curves in the range between 0.0 and 0.3Hz. Then, a starting point value of 0.3Hz should be selected because the noise stopped affecting the normal trend of the three curves simultaneously. This algorithm should be capable to detect these changes on the curves when analysing different signals and take this starting value as an input parameter to start the other calculations. Thank you for your attention.