Having issue displaying the result of a set of if statements

Question

Nasser Ramsis 2015-8-3

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/232078-having-issue-displaying-the-result-of-a-set-of-if-statements

回答： Walter Roberson 2015-8-3

Hello i have an issue i want to display the variable "ans" im using disp(ans) and ive placed it at every point possible it doesnt seem to work. the code is as follows

function deraprox
%This program will find an approximate solution to the nth order
%derrivative of an nth order polynomial where n is 1-4
disp ('Please input a polynomial function')
disp ('please use the following format')
disp('a*x.^4+b*x.^3+c*x.^2+d*x+e')
disp('enter 0 if there is no coefficient to one of the variables')
f=input('type now ','s');
disp ('what is the order of derrivation you desire?')
n=input('type now ');
disp ('what is the number of terms in taylor series? (1 or 2)')
tn=input('type now ');
disp ('what method would you like to use? f, b, or c')
method=input('type now ','s');
disp(' what is the step size?')
h=input('type now ');
disp('what point would you like to evaluate?')
xi=input ('type now ');
x=((xi-5*h):h:(xi+5*h));
y=eval(f);
fxim5=y(1,1);
fxim4=y(1,2);
fxim3=y(1,3);
fxim2=y(1,4);
fxim1=y(1,5);
fxi=y(1,6);
fxip1=y(1,7);
fxip2=y(1,8);
fxip3=y(1,9);
fxip4=y(1,10);
fxip5=y(1,11);
if method=='f'
    if n==1
        if tn==1
            ans=(fxip1-fxi)/h
        else 
            ans=(-fxip2+4*fxi+1-3*fxi)/2*h
        end
    elseif n==2
        if tn==1
            ans=(fxip2-2*fxip1+fi)/(h*h)
        else
            ans=(-fxip3+4*fxip2-5*fxip1+2*fxi)/(h*h)
        end
    elseif n==3
        if tn==1
            ans=(fxip3-3*fxip2+3*fxip1-fxi)/(h*h*h)
        else
            ans=(-3*fxip4+14*fxp3-24*fxip2+18*fxip1-5*fxi)/(2*h*h*h)
        end
    else
        if tn==1
            ans=(fxip4-4*fxip3+6*fxp2-4*fxip1-fxi)/(h*h*h*h)
        else
            ans=(-2*fxip5+11*fxip4-24*fxip3+26*fxip2-14*fxip1+3*fxi)/(h*h*h*h)
        end
    end 
elseif method=='b'
    if n==1
        if tn==1
            ans=(fxi-fxim1)/h
        else
            ans=(3*fxi-4*fxim1+fxim2)/2*h
        end
    elseif n==2
        if tn==1 
            ans=(fxi-2*fxim1+fxim2)/(h^2)
        else
            ans=(2*fxi-5*fxim1+4*fxim2-fxim3)/(h^2)
        end
 elseif n==3
        if tn==1 
            ans=(fxi-3*fxim1+3*fxim2-fxim3)/(h^3)
        else
            ans=(5*fxi-18*fxim1+24*fxim2-14*fxim3+3*fxim4)/(2*(h^3))
        end
 elseif n==4
        if tn==1 
            ans=(fxi-4*fxim1+6*fxim2-4*fxim3+fxim4)/(h^4)
        else
            ans=(3*fxi-14*fxim1+26*fxim2-24*fxim3+11*fxim4-2*fxim5)/(h^4) 
        end
else
    if n==1
        if tn==1
             ans=(fxip1-fxim1)/(h*2)
        else
            ans=(-fxip2+8*fxip1-8*fxim1+fxim2)/(12*h)
        end
 elseif n==2
        if tn==1 
           ans=(fxip1-2*fxi_fxim1)/(h*h)
        else
            ans=(-fxip2+16*fxip1-30*fxi+16*fxim1-fxim2)/(12*h*h)
        end
elseif n==3
        if tn==1 
            ans=(fxip2-2*fxip1+2*fxim1-fxim2)/(2*h*h*h)
        else
            ans=(-fxip3+8*fxip2-13*fxip1+133*fxim1-8*fxim2+fxim3)/(8*h*h*h)
        end
elseif n==4
        if tn==1 
            ans=(fxip2-4*fxip1+6*fxi-4*fxim1+fxim2)/(h*h*h*h)
        else
            ans=(-fxip3+12*fxip2-39*fxip1+56*fxi-39*fxim1+12*fxim2-fxim3)/(64*h*h*h*h) 
        end
        end
    end
end