MATLAB : using fprintf in a loop

Posted on 2004-10-06
Last Modified: 2006-11-17
GOAL: I want to write a loop so that a text file is generated using data that has been stored in a series of systematically named MAT files.

The loop code is here:

openfile = strcat('CEA_costlevel',lev,'.txt');
out1 = fopen(openfile,'w')
createdate = datestr(now);

for run =  1:runs  
            runstr = int2str(run_num);
            printstring = strcat('nh_run =',runstr,'\tDate =',createdate,'\n');
            fprintf(out1, printstring);
            for strat_num = 1:strategies
                strat = int2str(strat_num);
                printstring = strcat('strat\tdis_cost\n');
                fprintf(out1, printstring);
                fprintf(out1,''%d\t%10.4f\n', strat_num, run_1strat_1.tot_dis_cost);

The problem is with the "fprintf" line. the variable names for the float variables are systematically named as follows. run_1strat_1.tot_dis_cost should be printed to the file in the first iteration of the loop, then run_1strat_2.tot_dis_cost in the next iteration, and run1strat_3.tot_dis_cost in the next, and so on till the inner and outer loop are exhausted.

In the other situations where I need to fprintf something, a made a string "printstring" first. But I can't figure out to make the printstring when there are formated float variables that need to be part of the string. I thought typing \' would let me insert a single quote but this doesnt work in MATLAB.

Thanks to anyone who can help me with this.

Question by:steveresch
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Expert Comment

ID: 12243570

it will be better use of array of float instead run_1strat_X.tot_dis_cost, isn't it?

Accepted Solution

PodExpert earned 350 total points
ID: 12245886
Hello Steve,

this can be done using eval function, which is present in almost every interpreted langugage (including Matlab Script). Try the following instead of the fprintf line:

myValue = eval(strcat('run_1strat_', int2str(strat_num), '.tot_dis_cost'));
fprintf(out1,''%d\t%10.4f\n', strat_num, myValue);

Note that eval(s) evaluates a string "s" as it was an ordinary matlab expression and returns its value. You can therefor use the "parametric" variable names you need - first, the variable name is created by concatenating "run_1strat_", integer strat_num converted to a strig, and ".tot_dis_cost". Then we evaluate it, get the result and send it to fprintf.

Good luck.

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