Change definition to include K^2 and PI^2

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>
Change definition of function "Calcula_Uxy"

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>
Change "matematica.c"

Change definition of K^2 and PI^2.
Change initialization of "Grade" "i" to "ny" and "j" to "nx".
Correct function to work with new "Grade".
Compact function "Calcula_Uxy".

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>
Change function to print "Grade" in "io.c"

Change function to print to work with modification of
initialization "Grade".

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>