MTH3051 Introduction to Computational Mathematics - User Web ...

School of Mathematical Sciences
Monash University
a = 2; b = 1; c = 5;
if ( abs(a) > 1e-10 )
if ( b*b - 4*a*c ) >= 0 )
r_1 = ( -b + (b*b - 4*a*c)^(1/2) )/(2*a) ;
r_2 = ( -b - (b*b - 4*a*c)^(1/2) )/(2*a) ;
else
r_1 = 0;
r_2 = 0;
end
else
r_1 = -c/b;
r_2 = r_1;
end;
The message here is never test two real numbers for equality. Thus if the mathematics
tells you something special happens when p = q (for example) then in your
Matlab code you should never use an if statement like
if (p == q)
· · ·
end
but rather
if abs(p - q) < very_small
· · ·
end
There still remains the niggling problem of how to handle the case where both a and b
are zero. Here I invoke the classic excuse of a lecturer – this case is left as an exercise
for the student.
2.3 A finite series
How would you get Matlab to compute the following sum
S = 1 + 1 2 + 1 3 + 1 4 + · · · + 1
100
This seems simple enough, just add up 100 numbers. Too easy really (agreed?). If you
were to compute this by hand (always a good place to start when writing computer code)
you most probably would start with the first term, add on the second term, then the
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