how to write correct looping

hi all

i want to read file and which is some condition

for data 1-100 is read properly

but i am confused why is the value in line X>99 i can not get rigth value

A=readfile('pf_ext_pcs_1_ts_1_t_1_000000_0.vtu')';
C = A(10217:13618);
C=cellfun(@(x)sscanf(x,'%f'),C,'UniformOutput',false);
format long g
pf=cell2mat(C);    % 0 represents fracture occurs
pf(pf<0.1) =10000; % 

km=nan(1000,1); % total cell permeability multiplier

a=1;
for x=1:10000
   km(x,:)=1/8*(pf(x,1)+pf(x+1,1)+pf(200+a,1)+pf(201+a,1)+pf(10201+a,1)+pf(10202+a,1)+pf(a+10401,1)+pf(a+10402,1));
   if x>99 &&x<199
     km(x,:)=1/8*(pf(201-a,1)+pf(202-a,1)+pf(302-a,1)+pf(303-a,1)+pf(10402-a,1)+pf(10403-a,1)+pf(10503-a,1)+pf(10504-a,1));

   elseif x > 199
         km(x,:)=1/8*(pf(302-a,1)+pf(303-a,1)+pf(403-a,1)+pf(404-a,1)+pf(10503-a,1)+pf(10504-a,1)+pf(10604-a,1)+pf(10605-a,1));
     
         elseif x > 299
             km(x,:)=1/8*(pf(403-a,1)+pf(404-a,1)+pf(504-a,1)+pf(505-a,1)+pf(10604-a,1)+pf(10605-a,1)+pf(10705-a,1)+pf(10706-a,1));
     

Answer 1

[Florian]

for x=1:10000
   if x<=99
       km(x,:)=1/8*(pf(x,1)+pf(x+1,1)+pf(200+a,1)+pf(201+a,1)+pf(10201+a,1)+pf(10202+a,1)+pf(a+10401,1)+pf(a+10402,1));
   elseif x>99 && x<=199
       km(x,:)=1/8*(pf(201-a,1)+pf(202-a,1)+pf(302-a,1)+pf(303-a,1)+pf(10402-a,1)+pf(10403-a,1)+pf(10503-a,1)+pf(10504-a,1));
   elseif x>199 && x<=299
       km(x,:)=1/8*(pf(302-a,1)+pf(303-a,1)+pf(403-a,1)+pf(404-a,1)+pf(10503-a,1)+pf(10504-a,1)+pf(10604-a,1)+pf(10605-a,1));
   else
       km(x,:)=1/8*(pf(403-a,1)+pf(404-a,1)+pf(504-a,1)+pf(505-a,1)+pf(10604-a,1)+pf(10605-a,1)+pf(10705-a,1)+pf(10706-a,1));
   end
end

[Walter Roberson]

for x=1:10000
   if x<=99
       km(x,:)=1/8*(pf(x,1)+pf(x+1,1)+pf(200+a,1)+pf(201+a,1)+pf(10201+a,1)+pf(10202+a,1)+pf(a+10401,1)+pf(a+10402,1));
   elseif x<=199
       km(x,:)=1/8*(pf(201-a,1)+pf(202-a,1)+pf(302-a,1)+pf(303-a,1)+pf(10402-a,1)+pf(10403-a,1)+pf(10503-a,1)+pf(10504-a,1));
   elseif x<=299
       km(x,:)=1/8*(pf(302-a,1)+pf(303-a,1)+pf(403-a,1)+pf(404-a,1)+pf(10503-a,1)+pf(10504-a,1)+pf(10604-a,1)+pf(10605-a,1));
   else
       km(x,:)=1/8*(pf(403-a,1)+pf(404-a,1)+pf(504-a,1)+pf(505-a,1)+pf(10604-a,1)+pf(10605-a,1)+pf(10705-a,1)+pf(10706-a,1));
   end
end

You had to fail x<=99 to reach the first elseif . There are several ways to fail x<=99:

1. x is non-scalar and has a mix of values. However, in a for x=1:10000 you can be sure that x will be numeric scalar
2. x is nan, because comparing nan to anything is false, including nan == nan is false as is nan ~= nan. But we are in a for x = integer vector loop, so we know x will not be nan
3. x <= 99 fails because x is a numeric scalar that is > 99

We can rule out the first two cases by context, leaving x > 99 . So the first elseif will only be reached if x > 99. And that being the case, it is not productive to test x>99 in the elseif: if it were false, then we could not have reached the elseif (under the pre-condition of integer scalar for loop)