For Loop range error

I am running the following for-loop to evaluate over a range of time, over 0.5s steps. But when I run the function it gives me a result I cant comprehend. The result is evaluated over steps of 0.0005s, I have no clue why it is this way. Can someone please help?

   Tab=[];
    for t= -5.0:0.5:50.0 %s
        if t>=0 & t<=10
            v=(11*(t^2))-(5*t)
        elseif t>=10 & t<=20
            v=1100-(5*t)
        elseif t>=20 & t<=30
            v=(50*t)+2*((t-20)^2)
        elseif t>30
            v=1520* exp(-0.2*(t-30))
        else 
            v=0
        end
        Tab=[Tab; t   v]    
    end
    

Tab

Result:

Tab =

1.0e+03 *

-0.0050 0

-0.0045 0

-0.0040 0

-0.0035 0

-0.0030 0

-0.0025 0

-0.0020 0

-0.0015 0

-0.0010 0

-0.0005 0

0 0

0.0005 0.0003

0.0010 0.0060

0.0015 0.0173

0.0020 0.0340

0.0025 0.0563

0.0030 0.0840

0.0035 0.1172

0.0040 0.1560

0.0045 0.2003

0.0050 0.2500

0.0055 0.3053

0.0060 0.3660

0.0065 0.4323

0.0070 0.5040

0.0075 0.5813

0.0080 0.6640

0.0085 0.7522

0.0090 0.8460

0.0095 0.9453

0.0100 1.0500

0.0105 1.0475

0.0110 1.0450

0.0115 1.0425

0.0120 1.0400

0.0125 1.0375

0.0130 1.0350

0.0135 1.0325

0.0140 1.0300

0.0145 1.0275

0.0150 1.0250

0.0155 1.0225

0.0160 1.0200

0.0165 1.0175

0.0170 1.0150

0.0175 1.0125

0.0180 1.0100

0.0185 1.0075

0.0190 1.0050

0.0195 1.0025

0.0200 1.0000

0.0205 1.0255

0.0210 1.0520

0.0215 1.0795

0.0220 1.1080

0.0225 1.1375

0.0230 1.1680

0.0235 1.1995

0.0240 1.2320

0.0245 1.2655

0.0250 1.3000

0.0255 1.3355

0.0260 1.3720

0.0265 1.4095

0.0270 1.4480

0.0275 1.4875

0.0280 1.5280

0.0285 1.5695

0.0290 1.6120

0.0295 1.6555

0.0300 1.7000

0.0305 1.3754

0.0310 1.2445

0.0315 1.1260

0.0320 1.0189

0.0325 0.9219

0.0330 0.8342

0.0335 0.7548

0.0340 0.6830

0.0345 0.6180

0.0350 0.5592

0.0355 0.5060

0.0360 0.4578

0.0365 0.4142

0.0370 0.3748

0.0375 0.3392

0.0380 0.3069

0.0385 0.2777

0.0390 0.2513

0.0395 0.2273

0.0400 0.2057

0.0405 0.1861

0.0410 0.1684

0.0415 0.1524

0.0420 0.1379

0.0425 0.1248

0.0430 0.1129

0.0435 0.1022

0.0440 0.0924

0.0445 0.0836

0.0450 0.0757

0.0455 0.0685

0.0460 0.0620

0.0465 0.0561

0.0470 0.0507

0.0475 0.0459

0.0480 0.0415

0.0485 0.0376

0.0490 0.0340

0.0495 0.0308

0.0500 0.0278

[Walter Roberson]

I do not see anything wrong at the moment?

I suggest that you command

 format long g

and look at the output again.

[Shantanu Chatterji]

Wow that worked!

Can you PLEASE explain what happened here? what and how does adding the line format long g help???

THANKS!!!

[Walter Roberson]

format long g does not change the calculation, only the way the output is displayed. You overlooked the early lines of the output

 Tab =
   1.0e+03 *

That means that you have to mentally multiply all of the displayed results by 1E3 (that is, 1000) to get the stored value, and that the portion of values less than 0.001*1E3 have been discarded for display purposes.

I personally wish that Mathworks would stop making format short the default. I have seen too many people caught by it.

[Shantanu Chatterji]

Thanks Walter, you are awesome!

Answer 1

[KSSV]

t0 = -0.5 ; % initial time 
t1 = 50 ;  % final time 
dt = 0.5 ;  % time step 
T = t0:dt:t1 ;  % create time vector 
N = length(T) ; % length of time steps 
Tab = zeros(N,1) ;  % initialize velocity 
for i = 1:N
    t = T(i) ; 
    if t>=0 && t<=10
        v=(11*(t^2))-(5*t) ; 
    elseif t>=10 && t<=20
        v=1100-(5*t) ; 
    elseif t>=20 && t<=30 
        v=(50*t)+2*((t-20)^2) ;
    elseif t>30
        v=1520* exp(-0.2*(t-30)) ; 
    else
        v=0 ; 
    end
    Tab(i,:) = v ; 
end