New to Matlab, need help

Question

Christopher 2013-12-17

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评论： kei hin 2013-12-19

Hi,

I'm really new to Matlab and I need some help with my homework. We are supposed to write a script/program that determines the zeros of a second degree polynomial function.

All I have so far is the basic structure:

a=input('Koeffizient a: ');
b=input('Koeffizient b: ');
c=input('Koeffizient c: ');
d=b^2-4ac
if d>0
x1=(-b+d)/2a;
x2=(-b-d)/2a;
if d=0
-(b/2a)
d<0
Fehler
      end
  end
  disp('Nullstelle ist: ')

I would appreciate any help (especially those in the form of pointers to help me solve the problem myself and not get you guys to do my homework :P )

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Answer 1

kei hin 2013-12-17

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编辑：kei hin 2013-12-17

Operators can't be omitted. If 'a=2', you want '4',then you need '2*a', not '2a'. And you'd better type your code in Matlab, you will see the tips or warning message from the Matlab to correct your code.

for 'disp' help

http://www.mathworks.com/help/matlab/ref/disp.html?searchHighlight=disp

You can also type 'doc' in matlab command window, then search something you want to know.

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Walter Roberson 2013-12-17

Remember to include () if needed. You probably want to divide by (2*a) rather than to divide by 2 and then multiply the result by a.

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Answer 2

Christopher 2013-12-17

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https://ww2.mathworks.cn/matlabcentral/answers/109964-new-to-matlab-need-help#answer_118647

编辑：Christopher 2013-12-17

在 MATLAB Online 中打开

I've worked on it a little more, but my main problem seems to be around the d>=0 part. Any tips?

if true
  % code
end
a=input('Koeffizient a eintippen: ');
b=input('Koeffizient b eintippen: ');
c=input('Koeffizient c eintippen: ');
d=(b*b)-(4*a*c);
if d>=0
  x1=(-b+d)/(2*a);
  if x1 ~=0; 
      disp (x1)
      disp('ist eine Nullstelle');
  end
  x2=(-b-d)/(2*a);
  if x2 ~=0; 
      disp (x2)
      disp('ist eine Nullstelle');
  end
  x3=-(b/(2*a));
  if x3 ~=0; 
      disp (x3)
      disp('ist eine Nullstelle');
  end
 else disp ('keine Loesung')