Error of the If command in the input bar

jospercomp shared this question 3 years ago

Answered

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I found an error of the if command when entering two domain restriction conditions for multivariable functions.

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I do not understand why if I put the command from the input bar it does not work and it produces an error message. But if I first enter the function without conditions in the input bar and then change it from the properties window the command does not give errors. If I place if nested in the input bar if they work.

If(x > 0, If(0 < y < 1, 5ℯ^(-3π² x) sin(π y)))

If(0 < y < 1, If(x > 0, 5ℯ^(-3π² x) sin(π y)))

The nested if graphs are not the same as the if graph with the conditions separately.

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In addition, the commands using and and or generate other graphics with restrictions.

If(x > 1 ∧ 0 < y < 1, 5ℯ^(-3π² x) sin(π y))

If(x > 1 ∨ 0 < y < 1, 5ℯ^(-3π² x) sin(π y))

The same question

Comments (11)

Michael Borcherds ● 3 years ago

Did you read the manual?

https://wiki.geogebra.org/e...

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jospercomp ● 3 years ago

The manual says nothing when the syntax of the if command is:If( <Condition 1>, <Condition 2>, <Then> )

I do not understand why this syntax works in Value Inputbox; but it is not working in Input bar.

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Michael Borcherds ● 3 years ago

this syntax works in Value Inputbox

Please post your .ggb file showing it "working"

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jospercomp ● 3 years ago

Input bar write:

5ℯ^(-3π² x) sin(π y)

In Value Textbox rewrite:If(x > 0, 0 < y < 1, 5ℯ^(-3π² x) sin(π y))

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Michael Borcherds ● 3 years ago

Please post your .ggb file showing it "working"

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jospercomp ● 3 years ago

This is ggb file.

Files: if_error_multiv...

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Michael Borcherds ● 3 years ago

You can combine conditions like this:

b(x, y) = If(x > 0 ∧ y > 0 ∧ y < 2, 5ℯ^(-3π² x) sin(π y))

This one works but you need to zoom in a little:

b(x, y) = If(x > 0 ∧ y > 0 ∧ y < 1, 5ℯ^(-3π² x) sin(π y))

Your file is using the syntax

If( <Condition>, <Then>, <Else> )

but not working as <Then> and <Else> are different object types

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mathmagic ● 3 years ago

I think this:

if(x>0,0<y<1,f) is read like if(x>0, function 1 when 0<y<1 otherwise 0,other wise f)

the second condition is interpreted as function defined with a boolean (0 or 1) value

see the plane zone at 1 high in your second image

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jospercomp ● 3 years ago

How can I write this syntax as a Geogebra command?

if(x>0, function 1 when 0<y<1 otherwise 0,other wise f)

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mathmagic ● 3 years ago

just like you have tried,ie:

a(x,y)=x^2+y^2

f(x, y) = If(x > 0, 0 < y < 3, a(x, y))

hide a

I used 3 because is more visible

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jospercomp ● 3 years ago

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