@tomleslie 

Dear tomleslie, 

Thank you for your answer. 

@tomleslie 

I realized that the problem replicates in your code when loading "Physics" package!

When I comment it out again, the program executed with no errors. I need the Physics package for differentiation in Lagrangian mechanics.

@tomleslie 

Thank you for your answer

1- The specifications given by the command version(): User Interface: 935137, Kernel: 922027, Library: 935137

2- I have loaded the package "Physics" for the rest of my code which is not included in the program yet.

3- Fortunately, your program gives the answer in my machine too as expected using 1D input, but my code does not work with 2D math input. It is so weird as you mentioned. I usually use 2D math input because it can be visualized and debugged better and is more clear for me to read. I re-upload the file again in 2D math input. Please do not execute the program to see the type of error which appears.

R2_Link_2D.mw

@tomleslie 

My OS is windows 10 64-bit and my Maple version is v18.01. I do not know how to extract the exact specifications such as kernel and so on.

@ecterrab 

Thank you for your response. With the with(Physics,diff) the problem solved.

@John Fredsted 

Please see the attached file under this response and do not run the program. The error messages are available. I think Maple in my system fails.

Q1.mw

@John Fredsted 

Thank you for your answer, but the problem still exists with this change.

@Axel Vogt 

Thank you for your nice answer. My question is that, is the final answer (i.e. the output of evalf(%)) the correct answer of my original integration or in the procedure you stated, Maple made some simplifications such as removing some terms? I mean, can I trust the final answer of your procedure as the exact answer of my integration? Because I am a beginner in Maple and don't know the reason for using some of the commands such as combine(%, exp), collect(%,W) and etc. 

@Carl Love 

I just used floats to help Maple. Using symbols make the computations for Maple more difficult, I think.

@vv 

What do you mean by floats? What is your suggestion for modifying symbolic computations? Can you explain more with an example?

@vv 

The integrand is a function of "s" and "t" parameters. The mentioned arbitrary functions are a function of "s" or "t". I want to have an integration with respect to variable "s", as specified. Other unknown arbitrary functions that are a function of variable "t" are considered as constants. 

@tomleslie 

I uninstalled the program and reinstalled again and updated to the version 18.02 with the same build as you use. Fortunately, the problem solved and no error message came up. As you mentioned, this is weird that Maple returns an error for this simple matrix multiplication regardless what version actually has been used. Anyway, thank you for your answer.

@tomleslie 

Unfortunately, the problem persists after trying your 2 suggestions. As I stated, this problem does not occur when I copy the values of J_O_L1 and q_dot in another worksheet and Maple returns true but in this worksheet the error message appears. Following your first suggestion, there was no process called mserver.exe or maplew.exe after closing down all running Maple sessions. Following your second suggestion Maple returns the dimensions true i.e. 3*2 and 2*1. Please download the following file and do not run the code to see the error showing the condition of running the code in my system.

F2.mw

@Carl Love 

Maple 18.00, X86 64 WINDOWS, Feb 10 2014, Build ID 922027

@tomleslie 

How can I find the exact version of Maple as you mentioned in your response?