Overwriting specific in loop data before running runpf

[Marc Gebhardt]

Hi,

if i could minimize my problem in an easier case:

i specified my knots and branches in a case file of my matpower direction.
now i want to show the influence of varying one parameter of the branches.
for example the resistance of one line influences the losses.

so i bulit a for-loop, which should overwrite the input of the runpf
calculation.

how can i adress the workspace without changing the case-file every time?
my solution (lower in the text) doesn't work, cause it calculates every
time with the given value in the case-file.

clear all;
%loading of the given topology
run case_123.m;
%setting the steps
n=5;
stepsize=0.5;
%loop for the steps
for i=1:n;
    %calc the new resistance
    resis=-(n+1)/2*stepsize+stepsize*(i);
    %write it in the case (!!!!!!!!!!!!!!!!!!!!! and this is wrong)
    ans.branch(2,3)=resis;
    %doing the powerflowcalc
    mpRes=runpf('case_pst1');
    %output of the wanted values...
    output(i,1)=resis;
    output(i,2)=mpRes.branch(1,16);

end

how can i change the single value in a case with a loop for comparing the
results?

thank you
marc