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Assistance with solving coupled equations using module with external file

Mohsen Dayyani Kelisani

Mohsen Dayyani Kelisani, Deutsches Elektronen Synchrotron

Posted 6 months ago

Dear All, I am seeking your assistance in solving a system of two coupled equations using a Module that involves writing to and reading from an external file. To clarify my requirement, I have included an example program below that demonstrates my approach. However, the current implementation does not work as intended. Could you please help me identify and correct the issues in my program? Your guidance would be greatly appreciated. FF[xx1_, xx2_] := Module[ {xxx1 = xx1, xxx2 = xx2, FF1, FF2}, ClearAll[FileC]; FileC = "C:\\Mohsen-Files\\MLSF\\W-1\\MLSF.3\\MLSF\\C.txt"; OpenWrite[FileC]; WriteString[ FileC, Sin[xxx1], "\n", Cos[xxx2] ]; Close[FileC]; ClearAll[DataC]; DataC = Import[FileC, "Table"]; ClearAll[FF1, FF2]; FF1 = xxx1DataC[[1, 1]]; FF2 = xxx2DataC[[2, 1]]; {FF1, FF2} ]; FindRoot[ FF[x1, x2] == {0.0, 0.0}, {{x1, \[Pi]/4}, {x2, \[Pi]/4}} ]

POSTED BY: Mohsen Dayyani Kelisani

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Gianluca Gorni

Gianluca Gorni, University of Udine

Posted 6 months ago

The problem is `DataC[[1, 1]]` comes out as a string, not as an expression. Try FF = ToExpression[DataC[[1, 1]]] - xx; By the way, the local variables `xx` and `FF` are superfluous. I would rather write F[x_] := Module[{FileC, DataC}, FileC = "C:\Mohsen-Files\MLSF\W-1\MLSF.3\MLSF\C.txt"; OpenWrite[FileC]; WriteString[FileC, Tan[x]]; Close[FileC]; DataC = Import[FileC, "Table"]; ToExpression[DataC[[1, 1]]] - x];

The problem is DataC[[1, 1]] comes out as a string, not as an expression. Try

FF = ToExpression[DataC[[1, 1]]] - xx;

By the way, the local variables xx and FF are superfluous. I would rather write

F[x_] := 
  Module[{FileC, DataC}, 
   FileC = "C:\Mohsen-Files\MLSF\W-1\MLSF.3\MLSF\C.txt";
   OpenWrite[FileC];
   WriteString[FileC, Tan[x]];
   Close[FileC];
   DataC = Import[FileC, "Table"];
   ToExpression[DataC[[1, 1]]] - x];

POSTED BY: Gianluca Gorni