@Markiyan Hirnyk 

@Preben Alsholm

Thank you for your help, but i still have one last question.

The output of fdiff is a number, essentially it's a derivative for the certain point. Is there a way to write the output as a procedure or use a vector somehow to be able to plot the graph of the derivatives?

So far i have an idea to use an array and some loop (while/for/does not matter), but i'd like to know if there is a simplier way to do this.

Here is basically what i'm trying to do and i'm having a problem with fdiff.

 example.mw

@Markiyan Hirnyk 

I'm having a trouble making this example work as well as understanding it.

So as far as i understood:

After i use pdsolve i have to write the output as a procedure.

The output is used in fdiff afterwards to get a derivative.

Is this correct?

Can you please give an example (assuming it's correct)?

@Carl Love 

Hello thank you for responding.

I'm going to send a simplified version of my code.

test1.mw

regarding certain points:

1. it's a random integer

2. i need to solve a system in which they are coupled but i have noticed that the problem is present even when they are not

4 This was really helpful, now i know that the problem lies within boundary conditions. The further those positions are the more stretched the resulting graph is.  However these are stand-ins for infinity, yes. These boundary conditions are critical for my solution though.

Anyway varying spacestep seems to help but i don't get the expected result with this. What is the best way to set boundary conditions then?