warm start in AMPL API

[mahraz amini]

Hi all

suppose I have a variable 

var Pcharge  {BUS , Time};

and

set BUS := {1 2};

set Tiem := { 1 2 3};

I am wondering in AMPL API how I can give a matrix like Z as an initial solving point to the solver

Z = [ 1 2 3 ; 4 5 6];

Thanks.

[mahraz amini]

I should add that in the ampl api documentation it is said that I can do this like

    ampl.eval('var x;');

    x = ampl.getVariable('x');

    x.setValue(4);

so when I do the same I get this error:

    Error using VariableBase/setValue (line 296)

    No method 'setValue' with matching signature found for class 'com.ampl.Variable'.

    Error in Entity/subsref (line 73)

                    builtin('subsref',self,key);

Can anyone tell me how I can fix this please?

Thanks.

[AMPL Google Group]

Regarding your first question, you can provide an initial solution as follows:
BUS = {1, 2};
Time = {1, 2, 3};
df = DataFrame(2, 'BUS', 'Time', 'Pcharge');

Z = [1 2 3 ; 4 5 6]

df.setMatrix(Z, BUS, Time);
ampl.setData(df)
ampl.eval('display Pcharge;')

Regarding your second question, we were not able to reproduce this issue. Are you using the latest version of the API?
>> ampl = AMPL()

>> ampl.eval('var x;');
>> x = ampl.getVariable('x');
>> x.setValue(4);

>> ampl.eval('display x;')
x = 4

Best regards,
Filipe

--
Filipe Brandão
am...@googlegroups.com

{#HS:566357284-5856#}

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[mahraz amini]

Hi

thanks for you response. let me clear a little bit what I said before. the example that I posted works fine

ampl = AMPL()

ampl.eval('var x;');

x = ampl.getVariable('x');
x.setValue(4);

ampl.eval('display x;')
x = 4

 but when instead of the one variable I used vector variable it can not do the same

ampl.eval('var x {1..4};')

x = ampl.getVariable('x');

x.setValue([1 2 3 4])

Error using VariableBase/setValue (line 296)

No method 'setValue' with matching signature found for class 'com.ampl.Variable'.

Error in Entity/subsref (line 73)

                    builtin('subsref',self,key);

so is there any way that we can initialize variables with size more than 1, in the same way?

Thanks

Mahraz

[AMPL Google Group]

According to the documentation, the correct method for indexed entities would be setValues instead of setValue. However, Variable.setValues is apparently missing from the current implementation of the API and a new release is necessary to fix this issue. Nevertheless, you can do the same by creating a DataFrame with two columns, one for the index and another for the values (named after the variable you want to set), and set the variable values with ampl.setData as follows:

ampl.eval('var x {1..4};');
index = {1; 2; 3; 4};
values = {-5; -9; 2; 24};
df = DataFrame(1, 'index', 'x'); % the second column is named after the variable you want to set
df.setMatrix(values, index)
ampl.setData(df)

Best regards,
Filipe

--
Filipe Brandão
am...@googlegroups.com

{#HS:566357284-5856#}

On Mon, Apr 23, 2018 at 1:16 PM UTC, Ampl Modeling Language <am...@googlegroups.com> wrote:

Hi

[mahraz amini]

thank you very much for your response. 

if instead of a vector of size 4, we have a vector for example with size of 1000, then I wonder if there is a way to avoid writing {1;2;3;4;5;6;7;8;9;...;1000} and same for the values.

Thanks,

Mahraz

[AMPL Google Group]

You can use the MATLAB function num2cell (see, e.g., https://www.mathworks.com/help/matlab/ref/num2cell.html) to convert an array to a cell array and do the following:

ampl.eval('var x {1..1000};');
index = num2cell(1:1000);
values = num2cell([-4, -3, -2, -1, ...]);

df = DataFrame(1, 'index', 'x');

df.setMatrix(values, index)
ampl.setData(df)

Best regards,
Filipe

--
Filipe Brandão
am...@googlegroups.com

{#HS:566357284-5856#}

On Mon, Apr 23, 2018 at 7:15 PM UTC, Ampl Modeling Language <am...@googlegroups.com> wrote:

thank you very much for your response.

if instead of a vector of size 4, we have a vector for example with size of 1000, then I wonder if there is a way to avoid writing {1;2;3;4;5;6;7;8;9;...;1000} and same for the values.

Thanks,

Mahraz

On Mon, Apr 23, 2018 at 5:23 PM UTC, AMPL Google Group <am...@googlegroups.com> wrote:

According to the documentation, the correct method for indexed entities would be setValues instead of setValue. However, Variable.setValues is apparently missing from the current implementation of the API and a new release is necessary to fix this issue. Nevertheless, you can do the same by creating a DataFrame with two columns, one for the index and another for the values (named after the variable you want to set), and set the variable values with ampl.setData as follows:

ampl.eval('var x {1..4};');
index = {1; 2; 3; 4};
values = {-5; -9; 2; 24};
df = DataFrame(1, 'index', 'x'); % the second column is named after the variable you want to set
df.setMatrix(values, index)
ampl.setData(df)

Best regards,
Filipe

--
Filipe Brandão
am...@googlegroups.com