Why is the FOR loop in my program producing empty matrices? - scilab

Question

I am having a problem running a spiking-neuron simulator. I keep getting the error message, "operation +: Warning adding a matrix with the empty matrix will give an empty matrix result." Now I'm writing this program in "Scilab," but I'm hoping the problem I am having will be clear for the educated eye regardess. What I am doing is converting an existing MATLAB program to Scilab. The original MATLAB program and an explanation can be found here: https://www.izhikevich.org/publications/spikes.pdf
What happens in my Scilab version is that the first pass through the loop produces all the expected values. I Know this becuase I hit pause at the end of the first run, right before "end," and check all the values and matrix elements. However, if I run the program proper, which includes a loop of 20 iterations, I get the error message above, and all of the matrix values are empty! I cannot figure out what the problem is. I am fairly new to programming so the answer may be very simple as far as I know. Here is the Scilab version of the program:
Ne=8; Ni=2;
re=rand(Ne,1); ri=rand(Ni,1);
a=[0.02*ones(Ne,1); 0.02+0.08*ri];
b=[0.2*ones(Ne,1); 0.25-0.05*ri];
c=[-65+15*re.^2; -65*ones(Ni,1)];
d=[8-6*re.^2; 2*ones(Ni,1)];
S=[0.5*rand(Ne+Ni,Ne), -rand(Ne+Ni,Ni)];
v=60*rand(10,1)
v2=v
u=b.*v;
firings=[];
for t=1:20
I=[5*rand(Ne,1,"normal");2*rand(Ni,1,"normal")];
fired=find(v>=30);
j = length(fired);
h = t*ones(j,1);
k=[h,fired'];
firings=[firings;k];
v(fired)=c(fired);
u(fired)=u(fired)+d(fired);
I=I+sum(S(:,fired),"c");
v=v+0.5*(0.04*v.^2+5*v+140-u+I);
v=v+0.5*(0.04*v.^2+5*v+140-u+I);
u=u+a.*(b.*v-u);
end
plot(firings(:,1), firings(:,2),".");
I tried everything to no avail. The program should run through 20 iterations and produce a "raster plot" of dots representing the fired neurons at each of the 20 time steps.

Answer 1

You can add the following line
oldEmptyBehaviour("on")
at the beginning of your script in order to prevent the default Scilab rule (any algebraic operation with an empty matrix yields an empty matrix). However you will still have some warnings (despite the result will be OK). As a definitive fix I recommend testing the emptyness of fired in your code, like this:
Ne=8; Ni=2;
re=rand(Ne,1); ri=rand(Ni,1);
a=[0.02*ones(Ne,1); 0.02+0.08*ri];
b=[0.2*ones(Ne,1); 0.25-0.05*ri];
c=[-65+15*re.^2; -65*ones(Ni,1)];
d=[8-6*re.^2; 2*ones(Ni,1)];
S=[0.5*rand(Ne+Ni,Ne), -rand(Ne+Ni,Ni)];
v=60*rand(10,1)
v2=v
u=b.*v;
firings=[];
for t=1:20
I=[5*rand(Ne,1,"normal");2*rand(Ni,1,"normal")];
fired=find(v>=30);
if ~isempty(fired)
j = length(fired);
h = t*ones(j,1);
k=[h,fired'];
firings=[firings;k];
v(fired)=c(fired);
u(fired)=u(fired)+d(fired);
I=I+sum(S(:,fired),"c");
end
v=v+0.5*(0.04*v.^2+5*v+140-u+I);
v=v+0.5*(0.04*v.^2+5*v+140-u+I);
u=u+a.*(b.*v-u);
end
plot(firings(:,1), firings(:,2),".");

Answer 2

The [] + 1 is not really defined in a mathematical sense. The operation might fail or produce different results depending on the software you use. For example:
Scilab 5 [] + 1 produces 1
Scilab 6 [] + 1 produces [] and a warning
Julia 1.8 [] .+ 1 produces [] but [] + 1 an error.
Python+Numpy 1.23 np.zeros((0,0)) + 1 produces [].
I suggest checking with size() or a comparison to the empty matrix to avoid such strange behaviour.