**Advice: **
Assume doesn't affect solve

The assume command is used with symbolic variables that are not assigned values, and tells Maple that it can apply rules that would be appropriate when the variable has certain properties (e.g. is an integer). This primarily affects the
**simplify**
command. Thus if
**x**
is assumed to be positive,
can be simplified to
.

However, these assumptions do not restrict the values for
**x**
that can be returned by
**solve**
and its related commands. There are other ways to restrict these values.

** Examples:**

`> `
**assume(x, positive);**

`> `
**simplify(sqrt(x^2));**

In this example,
**solve**
finds both real and complex solutions; the assumption on
**x**
has no effect.

`> `
**solve(x^4 + 2*x = 20, x);**

Finding positive solutions in "solve":

`> `
**solve({y^4 + 2*y = 20, y > 0}, y);**

Finding real solutions:

`> `
**solve({y^4 + 2*y = 20, y > -infinity}, y);**

Finding integer solutions:

`> `
**isolve(y^4 + 2*y = 20);**

Real (numerical) solutions with
**fsolve**
:

`> `
**fsolve(y^4 + 2*y = 20, y);**

Restricting to an interval:

`> `
**fsolve(y^4 + 2*y = 20, y = 0 .. infinity);**

Another option for
**fsolve**
is
**avoid = {variable = value, ...}**
which causes
**fsolve**
to omit one or several known solutions. This is especially useful for non-polynomial equations where
**fsolve**
only returns one solution.

`> `
**fsolve(y^3 + 2 = 20/y, y);**

`> `
**fsolve(y^3 + 2 = 20/y, y, avoid = {y=2});**

However, the
**avoid**
option doesn't seem to work for systems of equations:

`> `
**fsolve({x+2*y=2,x^2-y^2=0},{x,y}, avoid={x=-2.000000000,y=2.000000000});**

`> `
**fsolve({x+2*y=2,x^2-y^2=0},{x,y}, x=0..infinity);**

**See also:**
__assume__
,
Declaring the type of an argument
,
__fsolve__
,
__isolve__
,
__solve__

**Maple Advisor Database**
R. Israel, 1997