print 1-D array to file as 2-D matrix

Dear colleagues:

I have a 1-D array, named pvar, where contains the "primary variables" generated in a method-of-lines PDE simulation of a one-dimensional advection-diffusion-reaction system. pvar has nx npde columns, where nx is the number of node points in the one-dimensional spatial domain, and npde is the number of PDEs in the system. I would like to print pvar out as 2-D matrix, row by row to a text file, along with 1-D array x that contains the node points for the one-dimensional spatial domain. An updated version of pvar is generated at each time step in the simulation, and I want to print that updated array along with x at selected output times using the outputfcn in the Matlab ODE solvers. I have done this type of print-to-file in Fortran versions of this same type of simulation using the following statement:

do i=1,nx

j=npde * i

write(1,*) x(i),(pvar(j-k)),k=(npde-1),0,-1)

end do

where the statement pvar(j-k)),k=(npde-1),0,-1 writes the values for each PDE, going left to right, for each node point going down through the nx nodes points in sequence.

What I don't know how to do is to code this statement in Matlab. The first thing I tried was

for i=1:nx

j=npde*i;

fprintf(fid,'%g\t',x(i),pvar(j-(npde-1):-1:0);

end

Which returns the error statement "Array indices must be positive integers or logical values"

I'm not sure if there is a vectorized coding structure available in Matlab which does the same thing as that in Fortran, but if there is, could some one please enlighten me?

Many thanks,

Eric Roden

Professor of Geoscience

University of Wisconsin-Madison

[Stephen23]

"I want to print that updated array along with x at selected output times using the outputfcn in the Matlab ODE solvers."

In most cases, as Walter Roberson wrote, "Doing that would be a mistake":

https://www.mathworks.com/matlabcentral/answers/1872692-how-to-store-intermediate-values-of-solution-in-ode45#answer_1121852

https://www.mathworks.com/matlabcentral/answers/429179-how-do-i-extract-an-intermediate-variable-calculated-and-used-inside-my-ode45-function#answer_346298

https://www.mathworks.com/matlabcentral/answers/92701-how-do-i-pass-out-extra-parameters-using-ode23-or-ode45-from-the-matlab-ode-suite#comment_462587

https://www.mathworks.com/matlabcentral/answers/396633-how-to-store-a-intermediate-variable-from-ode45-function-to-the-workspace-as-a-vector#answer_316584

https://stackoverflow.com/questions/60619524/is-there-a-way-to-output-intermediate-calculations-of-an-ode-solver-in-matlab

[Stephen23]

"I'm not sure if there is a vectorized coding structure available in Matlab which does the same thing as that in Fortran,"

The general MATLAB approach is to use arrays, not to write lots of nested loops. As far as I can tell you have a matrix: then probably all you need is transpose/reshape or similar, and then one FPRINTF call.

[Adam Danz]

formattedDisplayText may come in handy.