trouble plotting driving style from acceleration

clc; 
clear all;
Mydata2=xlsread('Log_U0006387_160311_740d0.csv');
t=Mydata2(:,1);
v=Mydata2(:,3)*1.60934*1000/3600;
a = diff(v)./diff(t)
diff(v);
if a <0
    a=inv(a);   %To receive positive values for acceleration
end
if a < 0.7
    ds_mapping = 0
end
for i = 1:length(a)
    if a(i) >= 0.7
        ds_mapping = 1;
    elseif a <= 2.81
        ds_mapping = 2;
    elseif a <= 3.65
        ds_mapping = 3;
    end
end
yyaxis left
plot(t(2:end),a , 'r')
xlabel('time')
ylabel('Acceleration');
hold on
yyaxis right
plot(t(2:end),ds_mapping , 'b')
ylabel('DS');
hold off
grid on

this is the code I currently have i'm trying to plot the driving style between those ranges however, my answer keeps returning to zero

[Dyuman Joshi]

1 - You need to store ds_mapping as a vector.

2 - Why are you comparing a vector against a scalar?

if a <0
%
if a < 0.7

3 - Why are you taking inverse of a vector?

a=inv(a);   %To receive positive values for acceleration

Did you want to get the absolute value of real numbers? Then simpy use abs

[Gurjeevan]

so essentially I have calculated values for acceleration, there should be an image of what the question looks like. What I now need to do is store those values and then plot them on a graph that looks like the one shown in the images. I did not know i was comparing a vector to a scalar. I am taking the inverse of a as i want the absolute values when I used abs(a) it wasn't working for some reason. How do i store ds_mapping as a vector?

[Gurjeevan]

[Gurjeevan]

[Dyuman Joshi]

"How do i store ds_mapping as a vector?"

Check out the documentation of for loop, as the hint suggests.