@vv Thank you

@mmcdara Many thanks

@Christopher2222 

There was not the creation of a sample, but the determination of its size.

How, for example, is done here

https://www.surveysystem.com/sscalc.htm

Thank you for your answers and help.

@DSkoog 

Indeed, the problem was that this package was not installed. Thanks for the detailed answer. Everything turned out.

@Markiyan Hirnyk 

This is the problem that I can not find the help page.

Tried here, unsuccessfully http://www.maplesoft.com/support/help/search.aspx?term=haar&pr=All

Why does not it work for

[Haar(1, 2, x)], x = 0 .. 1

@

I do not know whether it will be useful, but the disconnect with(Operators).

See test_ek.mw

Download test_ek.mw

@Ramakrishnan 

At first glance, it does not understand the value and units of measure the density of steel.

@vv 

How do you show it

Perhaps the problem in my software, what could be the reason for such behavior Maple?

@tomleslie 

Thanks for the response and assistance

To solve this equation in the general form (without boundary conditions) tried to use a command pdsolve, but without success.

@vv 

I can not understand what it means to a method for determining the box as a surface to calculate the flow. How to define where located this box. For example, with a sphere understanding, are the coordinates of the center and radius. I'm confused.

@vv 

Thanks for the reply and the link.

@acer 

Thanks, but I mean, how to calculate numerically (approximately) integral that can not be evaluated in closed form.

I'm sorry if I expressed myself not clear enough.

Thank you all for your help and participate in the discussion of this topic.

Slightly changed the first component of the field. Flux command is now working, but the same result. What could be the reason?

Also tell me how to calculate it numerically (mentioned it rlopez)

flux32.mw