Example 1
One common way this error can occur is if you try to use a name as a variable, but earlier that name was assigned a value.
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Solution:
Unassign .
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| (2.3) |
Example 2
In the following example, the equation is assigned to the name, which is passed as an argument to the int command. As indicated on the int/details help page, int accepts only an algebraic expression or operator as a first argument in all of the listed calling sequences. Thus, passing an equation to int results in an error.
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| (2.8) |
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Solution:
Assigning the algebraic expression instead of the equation corrects the error.
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| (2.14) |
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| (2.15) |
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Example 3
In the following example, the error that generates the error message is more subtle. The calling sequences of dsolve, as listed on the dsolve only an ordinary differential equation or a set or list of differential equations. In this example, a set of a set of equations is passed to dsolve instead of a set of equations.
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| (2.17) |
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| (2.18) |
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Error, (in dsolve) invalid arguments; expected an equation, or a set or list of them, received: {{diff(diff(f1(x), x), x)-f1(x)+f2(x) = 0, diff(diff(f4(x), x), x)+f3(x)-f4(x) = 0, diff(diff(f2(x), x), x)-2*f2(x)+f3(x)+f1(x) = 0, diff(diff(f3(x), x), x)-2*f3(x)+f4(x)+f2(x) = 0}}
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Solution:
One way to correct the above error is to remove the brackets around the sequence of differential equations assigned to
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| (2.20) |
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| (2.21) |
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| (2.22) |