Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 1-by-1-by-2.

I keep getting the above error when i run the below code. I have no clue on how to fix it. Its is pretty short code.

If anyone can assist, i will appreciate.

Thanks

%%
mo=4*10^-11; %initial particle mass in gCOD
Mx=7.2*10^-11; %maximum particle biomass 
rho=32000; %maximum density of particles in gCOD/cubic metre of particles

Rp=(3*mo/(4*pi*rho))^1/3;
Rn=Rp;
%%
k=1*10^-6;
x1(1,1,1)=k;%initial pos AOB
x2=x1+1*10^-6; %initial pos Nitrobacter
x3=x2+1*10^-6; %initial pos Nitrospira
x4=x3+1*10^-6; %initial pos CMX
x5=x4+1*10^-6; %initial pos AMX
x6=x5+1*10^-6; %initial pos het

sum1(1,1,1)=0.0;
sum2=0.0;

cell=0.8*10^-6;

r=0:7.5;
l=0:14;
c=0:109.8232;
deltaxj(1,1,1)=k;
x1New(1,1,1)=x1;

 for i=1:length(r)
        for ii=1:length(l)
           for iii=1:length(c)
               
               dn(i,ii,iii)=sum1+(x1-x1New)^2;
               deltaxj(i,ii,iii)=sum1+(x1-x1New)*(k.*(Rn+Rp)-dn)./dn;
               x1New(i,ii,iii)=x1-deltaxj;
               
           end
        end
 end

[Daniel Pollard]

If you format your code properly, it'll be much easier to read, and then easier to help you. What line does the error occur on? What were you expecting the code to output?

[Rik]

This time I edited your question for you. Next time, please use the tools explained on this page to make your question more readable.

You should use the debugger to step through your code and see what line changes the size or data type of your variables in an unexpected manner.

You are also dynamically growing variables, which becomes slow very fast. Pre-allocate array you can determine the size for:

dn=zeros(numel(r),numel(l),numel(c));
deltaxj=zeros(size(dn));
x1New=zerso(size(dn));
 for i=1:size(dn,1)
        for ii=1:size(dn,2)
           for iii=1:size(dn,3)

You should avoid length. Use numel or size instead. You should also avoid l and I variable names. Can you spot the differences at a glance?

Il1

[KIPROTICH KOSGEY]

Thank you @Rik, it is working !

I would have never been able to figure this out!

The final code below:

dn=zeros(numel(r),numel(l),numel(c));
deltaxj=zeros(size(dn));
x1New=zeros(size(dn));

 for i=1:size(dn,1)
        for ii=1:size(dn,2)
           for iii=1:size(dn,3)
               
               dn=sum1+(x1-x1New).^2;
               deltaxj=sum1+(x1-x1New).*(k.*(Rn+Rp)-dn)./dn;
               x1New=x1-deltaxj;
               
           end
        end
 end
 

[Rik]

The contents of your loop don't depend on the loop variables (unless one of them is a function). Is that the intention?

[KIPROTICH KOSGEY]

r , l and c are interdependent.

r represents z in the cartesian system, l represents x and c represent y.

The aim is to model bacterial colonisation of a wedge-shaped void. I am yet to introduce other functions.

Answer 1

[Daniel Pollard]

I haven't run it, but I think your code will error on the line

deltaxj(i,ii,iii)=sum1+(x1-x1New)*(k.*(Rn+Rp)-dn)./dn;

because deltaxj(i,ii,iii) is a number, so has one element, and dn is an array which grows with every iteration. You can't assign an array element to be equal to an array.

I suspect you intended

deltaxj(i,ii,iii)=sum1+(x1-x1New)*(k.*(Rn+Rp)-dn(i,ii,iii))./dn(i,ii,iii);

As a side note, please choose better names for your loop indices. Firstly, i is a bad variable name because it already has a built-in value, and secondly, it's difficult to tell at a glance what the difference between (ii,iii) and (iii,i) is (for example). If you really need to use that many nested loops (rather than vectorising your code), I'd suggest using k1, k2, k3, or similar.

[KIPROTICH KOSGEY]

Thanks @Daniel Pollard, but the suggestion did not work as it is still throwing errors the following error:

ndex in position 3 exceeds array bounds (must not exceed 1).

Error in Untitled (line 33)
               dn(i,ii,iii)=sum1+(x1-x1New(i,ii,iii)).^2;
   

However, the above suggestion by Rik does the trick!

Thanks a lot for the suggestion!

[Daniel Pollard]

Well x1new is a number, so trying to index it like x1new(i,ii,iii) will always return an error as soon as i, ii or iii are anything other than 1, which happens when the iii loop iterates around and tries to work with iii=2. The line with the error isn't even in the code you posted, it was right before so I had no reason to correct it for you!

Glad you found the solution in the end though.

[KIPROTICH KOSGEY]

Thanks @Daniel Pollard, I am still improving on what @Rik suggested, hope it will work when i include more parameters on the code.