@mehran rajabi Since partial derivatives always assume that the other variables are constant, what's the point of stating "when V is constant" and "when T is constant"?

@mehran rajabi And you can't figure out how to modify my Answer to get those? 

@tomleslie You've taken the derivative of both sides of the equation treating P as a constant or independent variable. That's not the same thing as (d^2 P) / (dT dV), etc. If you want to do it with diff rather than implicitdiff, you need to first substitute P(T,V) for P.

Since the first two of your three derivatives are necessarily equal (in symbolic computation), perhaps I don't understand your notation. Doesn't your Diff(P,T)[V] just mean Diff(P, [T,V])?

Thank you both. Control-Shift-R works as expected.

@reza gugheri Acer only means that he put a notation at the top of your Question as it appears on this site indicating that you are using Maple 13. No-one has yet reached a definite answer as to whether your problem can be solved by any version of Maple. I'm working on it, and my preliminary answer is that it can be solved (in terms of very complicated RootOf expressions), but the answers may be too long to be of much value.

@reza gugheri You've posted a worksheet and asked for an "answer" but you haven't asked a question.

@gaurav_rs Your input expression F1 has (if I counted correctly) 33 digits of precision in its coefficients. If you have Digits set to 10 when you input the expression, of course you'll get inaccurate results. My fast symbolic method can get you the full 33 digits of accuracy, which, of course is the most that you can expect given the coefficients. This accuracy can be confirmed by numeric integration, which is very robust for accuracy.

restart;
Digits:= 35:
F1:= #Lengthy input expression omitted.
#Fully symbolic integration (fastest way):
CodeTools:-Usage(
   int(fnormal(F1), [theta= Pi/4..7*Pi/4, r= 0..1])
);
memory used=57.39MiB, alloc change=-4.00MiB, cpu time=734.00ms, real time=736.00ms, gc time=125.00ms
                                                   12
           -1.1160010071917964702041524480427751 10  
#Inner integral symbolic, outer integral numeric:
CodeTools:-Usage(
   int(int(fnormal(F1), theta= Pi/4..7*Pi/4), r= 0..1, numeric)
);
memory used=169.19MiB, alloc change=140.01MiB, cpu time=1.59s, real time=1.81s, gc time=125.00ms
                                                   12
           -1.1160010071917964702041524480427751 10  
#Same thing with order of integration switched:
CodeTools:-Usage(
   int(int(fnormal(F1), r= 0..1), theta= Pi/4..7*Pi/4, numeric)
);
memory used=0.73GiB, alloc change=51.13MiB, cpu time=5.09s, real time=4.83s, gc time=843.75ms
                                                   12
           -1.1160010071917964702041524480427751 10  
#Fully numeric double integration:
Digits:= 15:
CodeTools:-Usage(
   int(fnormal(F1, 35), [theta= Pi/4..7*Pi/4, r= 0..1], numeric)
);
memory used=277.90MiB, alloc change=168.00MiB, cpu time=5.03s, real time=5.01s, gc time=234.38ms
                                         12
                     -1.11600100719180 10  

@HeiniKlum I changed the title for you. Hopefully I captured your intent.

@gaurav_rs How do come up with two decimal places? My result is far more accurate than that. I guarantee you that the discarded Bessel terms wouldn't change the 10000th decimal place of the result.

What you show is a standard Taylor polynomial (including order-of-approximation term) for sin centered at 1, such as you can find defined in any calculus textbook.

@Carl Love Well?? Does it work??? Since you didn't post the function, I have no way of knowing whether my idea corrected the problem unless you tell me.

@acer A small correction: The remainder is the fractional part times the divisor.

Yours is the third report of this problem that I've seen here. Someone said it was due to a "cracked" (illegal) copy of Maple. Since neither person reporting the error denied that, I'm inclined to believe it.

@nm Perhaps you didn't notice that the OP is asking about evalhf, not about evalf.