The plot(f,x) calling sequence plots the real function, f, a function of the independent variable, x, over a horizontal real range.

This warning occurs when the expression that you are trying to plot, using the plot(f,x) calling sequence, contains unexpected names.  

Example 1: Parametric plot

In this example, the variable names used as arguments for the real functions to be plotted do not match the variable name given to the range variable.

Solution: Changing one of the variable names to match the other solves this problem. Here, has been changed to

Example 2: Using e instead of exp

In this example, the letter e has been raised to a variable exponent, instead of using the calling sequence exp(x) to represent the exponential function.

Solution 1: To plot this expression, replace  with exp(x).

Solution 2: Alternatively, add from the Expression palette:

Example 3: Using pi instead of Pi

Solution:  For calculations, use "Pi" instead of "pi".

Example 4: using i instead of I

Maple uses I to represent one of the square roots of -1. If you want to create a complex expression, you need to use I.

Solution: Use Uppercase "I" instead of lowercase "i".

Example 5: unassigned value

The constant  has not been assigned a value.

Solution: Assign a value to

Example 6:

Similar to Example 5, in the list of expressions to be plotted, the first expression, contains an undefined constant.

Solution: Assign a value to

Example 7: 3-D plot example with wrong name used in function.

Solution:

plot, plot3d, plots[complexplot]