Loops and iterations?

[J Smart]

Hi,

Lets say that I have a species that have a random value attribute. These species are located on a grid, and there can be multiple agents from species on a single cell of the grid. 

I want each grid cell to calculate the sum of the species attribute. 

How do I do this? Is it something to do with loops or iterations?

I found how to make a list of the species inside the grid cell 

list<species> species_inside -> {species inside self}; 

but I'm not sure how to calculate the sum of the attribute of the species within the grid cell.

Thanks so much for your help,

J

[Benoit Gaudou]

Hi,

Let consider you have a species : 

species people {

  int my_attr;

}

If you have now the grid species plot, you can use the sum_of operator to compute the sum of an attribute value over a list / species of agents:

grid plot {

   reflex computation { 

      int  value -> (people inside self) sum_of (each.my_attr);

   }

}

Cheers

Benoit

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[J Smart]

On Wednesday, 11 December 2019 16:53:55 UTC+10, Benoit Gaudou wrote:

Hi,

Let consider you have a species : 

species people {

  int my_attr;

}

If you have now the grid species plot, you can use the sum_of operator to compute the sum of an attribute value over a list / species of agents:

grid plot {

   reflex computation { 

      int  value -> (people inside self) sum_of (each.my_attr);

   }

}

Cheers

Benoit

Le mer. 11 déc. 2019 à 13:24, J Smart <JayeNe...@gmail.com> a écrit :

Hi,

Lets say that I have a species that have a random value attribute. These species are located on a grid, and there can be multiple agents from species on a single cell of the grid. 

I want each grid cell to calculate the sum of the species attribute. 

How do I do this? Is it something to do with loops or iterations?

I found how to make a list of the species inside the grid cell 

list<species> species_inside -> {species inside self}; 

but I'm not sure how to calculate the sum of the attribute of the species within the grid cell.

Thanks so much for your help,

J

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[J Smart]

Hi Benoit,

Thank you for your response, but it is not working for me... this is the code, with an error in the grid species

global {

int nb_people <- 100;

init {

create people number: nb_people;

}

}

species people {

int my_attr <- rnd(0,5);

aspect circle {

draw circle(1) color: #orange;

}

}

grid plot width:10 height: 10 {

int value;

      reflex computation { 

      int value -> (people inside self) sum_of (each.my_attr);     // this line has the error "unknown facet function" 

   }

}

experiment Loops type: gui {

output {

display main_display {

grid plot lines: #green;

species people aspect:circle;

}

}

}

On Wednesday, 11 December 2019 16:53:55 UTC+10, Benoit Gaudou wrote:

Hi,

Let consider you have a species : 

species people {

  int my_attr;

}

If you have now the grid species plot, you can use the sum_of operator to compute the sum of an attribute value over a list / species of agents:

grid plot {

   reflex computation { 

      int  value -> (people inside self) sum_of (each.my_attr);

   }

}

Cheers

Benoit

Le mer. 11 déc. 2019 à 13:24, J Smart <JayeNe...@gmail.com> a écrit :

Hi,

Lets say that I have a species that have a random value attribute. These species are located on a grid, and there can be multiple agents from species on a single cell of the grid. 

I want each grid cell to calculate the sum of the species attribute. 

How do I do this? Is it something to do with loops or iterations?

I found how to make a list of the species inside the grid cell 

list<species> species_inside -> {species inside self}; 

but I'm not sure how to calculate the sum of the attribute of the species within the grid cell.

Thanks so much for your help,

J

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[Srirama Bhamidipati]

hi,

focus on the assignment operator ( <- ), it should not be ->

Srirama

[Jaye Newman]

Changing the assignment got rid of the error, but it still does not calculate the people attribute for each cell? I have attached an image of the simulation and highlighted where I expect it to calculate the attribute for the cell.

Here is the code:

global {

int nb_people <- 5;

init {
create people number: nb_people;
}
}
species people {
int my_attr <- rnd(0,5);

aspect circle {
draw circle(1) color: #orange;
}
}

grid plot width:6 height: 6 {

int value;

    reflex computation {
    int value <- (people inside self) sum_of (each.my_attr);
   }
}

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[Benoit Gaudou]

Dear Jaye,

I run your code on my GAMA 1.8.

If you look at your code, you should have a warning on the line inside the reflex computation.

grid plot width: 6 height: 6 {

int value;

reflex computation {

int value <- (people inside self) sum_of (each.my_attr);

}

}

The warning message is the following one :

This declaration of value shadows the declaration of an attribute of plot

First of all, in GAML (as in many language with type) there is a difference between a variable declaration and a value assignment.

The declaration is: int value;

The assignment is:  value <- 2;

Notice that you can do both on the same line: int value <- 2;

The important point is that declaring a variable creates a new object/variable whereas assigning a value to a variable only modifies an existing variable.

The second point is that  a variable exists only in the scope / in the block in which it is declared.

So if you declare a variable in a reflex, with:

reflex computation {

    int value <- 1;

}

This variable value exists only inside the reflex. In another reflex it does not exist.

So in your case, you declare a new variable in the reflex computation (that is thus different from the variable in the grid). You give it a value.

But this variable only exists during the execution of the reflex.

What introduces a confusion is that this variable has the same name as the variable/attribute of the grid plot. But GAMA considers that you create a new variable that shadows the existing attribute (as it has the same name).

A solution is to just transform the declaration+assignement in the reflex computation in a simple assignement (removing the int before value):

grid plot width: 6 height: 6 {

int value;

reflex computation {

     value <- (people inside self) sum_of (each.my_attr);

}

}

Cheers

Benoit

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[Jaye Newman]

Thanks Benoit,

This works for me. Thank you for your very clear and helpful response.

Cheers,

Jaye

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