IDEA: clear a-z cmd

[compsystems]

Hello sorry for my bad english

One of the problems for students, when a calculator as HP-PRIME or TI-89 stores a-z user variables, is that if one does not delete the variables, the results are evaluated, without showing the general or symbolic solutions.

See publication in the following link http://courses.wccnet.edu/~palay/math179/intslv92.htm

The TI68k have an option to remove the symbolic variables a-z, I think it would be a good option to incorporate it into the HP-PRIME for cas MODE, The RESTART CMD works but deletes all definitions =(, then a single command is required for the alphabetic variables, or expand RESTART CMD, accepting arguments RESTART([arg])

RESTART( "ALL" );
RESTART( "a-z" );








CAS VIEW

PHP Code:

CAS VIEW
CASE 1:  Preassigning values for x,y,z lowercase
x:=5; y:=6; z:=9;
//1.1: solve lowercase & Maximum simplify
solve( x^2*y+z*(-y-1) = 4*(x+z), x ); // returns 
{ (-√(598)+2)/6,  (√(598)+2)/6 }  // OK, As x,y,z have values, solve cmd solve then evaluate
approx(Ans); 
{  −3.742 , 4.409 }  // -> x=4.40 or x=−3.74 // ok

//1.2: SOLVE uppercase
SOLVE( x^2*y+z*(-y-1) = 4*(x+z), x );  or
SOLVE( x^2*y+z*(-y-1) = 4*(x+z), x, 6 );// returns 
4.40900642021 
SOLVE( x^2*y+z*(-y-1) = 4*(x+z), x, -6 );// returns 
−3.742 

CASE 2: Deleting variables x,y,z
purge(x,y,z); 
//2.1: solve lowercase
solve( x^2*y+z*(-y-1) = 4*(x+z), x );  // returns 
{ (√(y^2*z+5*y*z+4)+2)/y,   (-√(y^2*z+5*y*z+4)+2)/y } // Symbolic result for X1/2

{ (√(y^2*z+5*y*z+4)+2)/y, (-(√(y^2*z+5*y*z+4))+2)/y}|({y = 6,z = 9}); returns
{  4.409, −3.742  }


solve( x^2*y+z*(-y-1) = 4*(x+z), y );  // returns 
{(4*x+5*z)/(x^2-z)}// Symbolic result for Y
{(4*x+5*z)/(x^2-z)}|({x = 5,z = 9}); returns {65/16}

//2.2: SOLVE uppercase
SOLVE( x^2*y+z*(-y-1) = 4*(x+z), x, 6 );  returns "Error: Bad Guess(es)" 
SOLVE( x^2*y+z*(-y-1) = 4*(x+z), x, -6 ); returns "Error: Bad Guess(es)"
SOLVE( x^2*y+z*(-y-1) = 4*(x+z), y, -6 ); returns "Error: Bad Guess(es)"

CASE 3:  Non-zero values for X uppercase
X:=5; Y:=6; Z:=9;
//3.1: solve lowercase  
solve( X^2*Y+Z*(-Y-1) = 4*(X+Z), X); // returns 
{ (-√(598)+2)/6,  (√(598)+2)/6 }  // OK, As x,y,z have values, solve cmd solve then evaluate
approx(Ans); 
{  −3.742 , 4.409 }  // -> x=4.40 or x=−3.74 // ok

//3.2: SOLVE uppercase
SOLVE( X^2*Y+Z*(-Y-1) = 4*(X+Z), X);  or
SOLVE( X^2*Y+Z*(-Y-1) = 4*(X+Z), X, 6); // returns 
4.40900642021  
SOLVE( X^2*Y+Z*(-Y-1) = 4*(X+Z), X, -6);// returns 
−3.742  

CASE 4: Restting variables x,y,z
X:=0; Y:=0; Z:=0; 
//4.1: solve lowercase
solve( X^2*Y+Z*(-Y-1) = 4*(X+Z), X); // returns 
{ 0 }

//4.2: SOLVE uppercase
SOLVE( X^2*Y+Z*(-Y-1) = 4*(X+Z), X, 6);  returns
0 


HOME VIEW

PHP Code:

HOME VIEW
SOLVE(Eq, var, guess) // SOLVE CMD for HOME
CASE 5:
X:=5; Y:=6; Z:=9;
SOLVE( X^2*Y+Z*(-Y-1) = 4*(X+Z), X); returns 4.40900642021 
solve( X^2*Y+Z*(-Y-1) = 4*(X+Z), X);  returns {X}

CASE 6: Restting variables x, y, z
X:=0; Y:=0; Z:=0; 
SOLVE( X^2*Y+Z*(-Y-1) = 4*(X+Z), X); returns 4.40900642021
solve( X^2*Y+Z*(-Y-1) = 4*(X+Z), X); returns {X} 


[Arno K]

Is √(y^2*z+5*y*z+4)+2)/y different from √(598)+2)/6) with y=6 and z=9? No, so the result is correct.
So one has to be aware of the variables one has used before and then gets the desired symbolic results. I myself usually nearly never assign values to variables used in cas and have some rules I follow when I do so. Nevertheless the idea of spending purge some more parameters is not bad.
Arno

[cyrille de brébisson]

Hello,

One of the issue here is the meaning of the word "variable".

In symbolic math, a variable is a name used in replacement of an unknown value. In the symbolic word, a variable does not have any value (at least most of the time).

In lower grade math, in "computational" math, in physics or in programming worlds, a variable is a named container for a value. a Variable always has a value which it temporary replaces for clarity, readability or to allow a series of final computations with various values for the said variables.

Prime does have both these worlds in it. Home is definitely computational math. Cas is symbolic. But the 2 also interact to add to the confusion

The end result is Prime. Power and flexibility, but at the cost of the need to understand such subtility.

In your case, remember that by default, A-Z variables always have a value (computational) and a-z (lowercase) do not (symbolic). And you should be OK.

Hope this helps.

Cyrille

[KeithB]

That is fine for FORTRAN programmers that can use I for a loop variable, but what about us C programmers that have to use i? 8^)

I suggest that the OP write his own darn function/program if it is that important to him.

[compsystems]

The SOLVE in capital letters is not documented in the CATALOG HELP

Quote:solve
Returns a list of the solutions (real and complex) to a polynomial equation or a set of polynomial equations.

solve(Eq,[Var]) or
solve({Eq1, Eq2,…}, [Var]) or
solve(Eq, Var=Guess) or
solve(Eq, Var=Val1…Val2)

Quote:SOLVE
Solves an equation for one of its variables. Solves the equation En for the variable var, using the value of guess as the initial value for the value of the variable var. If En is an expression, then the value of the variable var that makes the expression equal to zero is returned.

SOLVE(En,var,guess)

This function also returns an integer that is indicative of the type of solution found, as follows:
0—an exact solution was found
1—an approximate solution was found
2—an extremum was found that is as close to a solution as possible
3—neither a solution, an approximation, nor an extremum was found

I do not understand the last part [0 - 3]

Update the examples of the first post, I think that THE DIFFERENT CASES should have a more detailed explanation by Bernard

[parisse]

solve(equation) solves equation with respect to x
solve(equation,var) solves equation with respect to var
solve([eq1,eq2,..],[var1,var2,...]) solve polynomial system with respect to var1,var2,...
The last syntaxes call the numeric solver, using an iterative method (var=guess) or bisection (var=a..b).

[compsystems]

SOLVE CMD in capitals should not evaluate after solving, when the variables are also capitals, because by default X, Y, ... are initialized to zero and there is no way to eliminate previously.

Please check the examples above

Thank you