I do not understand why I am getting permission denied trying to create a file.

restart;
fd := FileTools[Text][Open]("C:\\foo.txt", create=true,overwrite=true);

     Error, (in FileTools:-Text:-Open) permission denied

I am running the above on my PC, from Maple, using the same user which is me. I can ofcourse create a file on my C drive outside of Maple. So I do not understand why it says permission denied. Also tried "C:/foo.txt". Also tried

         fd := FileTools[Text][Open]("C:\\foo.txt", create,overwrite);

Any idea what can be the problem? and how to determine why it is giving this error? I am on windows 7, using Maple 2015.

http://www.maplesoft.com/support/help/maple/view.aspx?path=FileTools%2fText%2fOpen

http://www.maplesoft.com/support/help/maple/view.aspx?path=IO_errors

"permission denied" - An attempt was made to read from a file on which the user does not have
read permissions, or write to a file on which the user does not have write permissions."

Well, I do have write permission to make a file on my C drive !

I tried using fopen, and got same error

restart;
  try     
     fd := fopen("C:\\foo.txt",APPEND,TEXT);
  catch:
     print(`Unable to open file, error is`);
     print(StringTools:-FormatMessage(lastexception[2]));
  end try:

                 Unable to open file, error is
                      "permission denied"

So I have no idea why I keep getting permission denied.

Maple 2015:

simplify(1-2*sin(x)^2);  gives 2*cos(x)^2-1

I looked at help trying to understand why Maple thinks 2*cos(x)^2-1 is simpler than 1-2*sin(x)^2 but did not see it. I was expecting to see cos(2*x) as a result.

Is there a place to understand more Maple's simplification rules other than the help page? http://www.maplesoft.com/support/help/maple/view.aspx?path=simplify%2fdetails

Given this

z := -d*(y+a)+a;

and say we want to replace  a-a*d by c  so that the result is  c - d*y, but this does not work:

algsubs((a-a*d)=c,z);

since Maple does not "see" the d*a expression as it is not expanded yet.  Only when writing this it works:

algsubs((a-a*d)=c,expand(z));

At first I thought since this is an "algebraic" substitution, then Maple will figure it out on its own. But it seems that the expression being substititued has to explicity show there for it to work? Looking it help, it says

"Like subs, it does not expand products or powers before substitution"

So my question is: Is the rule of thumb when using algsubs, is to always expand the expression as in the above example?

Is there another Maple command or a package, which would have found this substition on its own? (i.e. without expanding first)

In Maple 2015:

restart;
with(Tolerances):
a:= 3 &+- 1;
b:= 2 &+- 1;
c:= 2 &+- 1;
solve(a*x^2+b*x+c=0,x);

gives "Error, (in evalr) improper op or subscript selector"

Is there a way to make it work with interval, i.e. Tolerances variables?  In Mathematica, the above works:

a = Interval[{2, 4}];
b = Interval[{1, 3}];
c = Interval[{1, 3}];
Solve[a*x^2 + b*x + c == 0, x]

Screen shot:

I was hoping to get similar result with Maple.  Is there differenet package/commands to work with interval variables in Maple that would support all operations if not this package?

These both work the same way

s1:=StringTools:-Join(["this is a ","test"]);
s2:=cat("this is a ","test");

When should one not use cat() command? It seems much simpler than Join. Are there cases where cat() will not work and Join will work?