I am having trouble saving a value and calculating new values from it.

my code is:

n = 180;
a = zeros(1,n);
a(1) = 20000;
R = 0.06;
r = R/12;
z = amortization(a(1),R,n);
for i = 2:n
    b(i) = a(i-1)*r;
    %b is interest payed in first month
    c = z-b(i);
    %c is amount applied towards loan principle
    a(i) = a(i-1)-c;
    %a is new amount left to  be paid
    d(i) = b(i)+b(i-1);
    %d is last month's interest plus this months
    e = b(1) + d(i);
    disp(e)
    x=1:180;
end

   100

  199.6561

  198.9667

  198.2738

  197.5775

  196.8777

  196.1743

  195.4675

  194.7571

  194.0432

  193.3257

  192.6046

  191.8799

  191.1516

  190.4196

  189.6840

  188.9447

  188.2017

  187.4550

  186.7046

  185.9504

  185.1924

  184.4307

  183.6651

  182.8958

  182.1225

  181.3454

  180.5644

  179.7795

  178.9907

  178.1980

  177.4012

  176.6005

  175.7958

  174.9871

  174.1743

  173.3575

  172.5365

  171.7115

  170.8823

  170.0490

  169.2116

  168.3699

  167.5241

  166.6740

  165.8196

  164.9610

  164.0981

  163.2309

  162.3593

  161.4834

  160.6031

  159.7184

  158.8293

  157.9357

  157.0377

  156.1352

  155.2281

  154.3165

  153.4004

  152.4797

  151.5544

  150.6244

  149.6899

  148.7506

  147.8066

  146.8579

  145.9045

  144.9463

  143.9834

  143.0156

  142.0429

  141.0654

  140.0830

  139.0957

  138.1035

  137.1063

  136.1041

  135.0969

  134.0847

  133.0674

  132.0450

  131.0175

  129.9849

  128.9471

  127.9041

  126.8560

  125.8025

  124.7438

  123.6798

  122.6105

  121.5359

  120.4558

  119.3704

  118.2795

  117.1832

  116.0814

  114.9741

  113.8613

  112.7429

  111.6189

  110.4892

  109.3540

  108.2130

  107.0664

  105.9140

  104.7558

  103.5919

  102.4222

  101.2466

  100.0651

   98.8777

   97.6844

   96.4851

   95.2798

   94.0685

   92.8511

   91.6276

   90.3981

   89.1623

   87.9204

   86.6723

   85.4180

   84.1573

   82.8904

   81.6172

   80.3375

   79.0515

   77.7590

   76.4601

   75.1547

   73.8428

   72.5243

   71.1992

   69.8675

   68.5291

   67.1840

   65.8322

   64.4737

   63.1083

   61.7362

   60.3571

   58.9712

   57.5783

   56.1785

   54.7717

   53.3578

   51.9369

   50.5089

   49.0737

   47.6314

   46.1818

   44.7250

   43.2609

   41.7895

   40.3108

   38.8246

   37.3310

   35.8299

   34.3214

   32.8053

   31.2816

   29.7503

   28.2113

   26.6647

   25.1103

   23.5481

   21.9781

   20.4003

   18.8146

   17.2210

   15.6193

   14.0097

   12.3921

   10.7663

    9.1324

    7.4904

    5.8401

    4.1816

plot(x, a,'b')
hold on
plot(x,e,'r')

function P = amortization(a, R, n)
r = R/12;

P = a*(r*((1+r)^n))/(((1+r)^n) - 1);
end

I am trying to plot the total accumulated interest paid (sum of b). so the correct plot would be (1,100), (2,199.66), etc. Any help would be appreciated. I am new to matlab.

Answer 1

[Voss]

n = 180;
a = zeros(1,n);
b = zeros(1,n);
e = zeros(1,n);
a(1) = 20000;
R = 0.06;
r = R/12;
z = amortization(a(1),R,n);
for i = 2:n
    b(i) = a(i-1)*r;
    %b is interest payed in first month
    c = z-b(i);
    %c is amount applied towards loan principle
    a(i) = a(i-1)-c;
    %a is new amount left to  be paid
    d(i) = b(i)+b(i-1);
    %d is last month's interest plus this months
    e(i) = e(i-1) + b(i);
end
x=1:180;
plot(x,a,'b')
hold on
plot(x,e,'r')

function P = amortization(a, R, n)
r = R/12;

P = a*(r*((1+r)^n))/(((1+r)^n) - 1);
end