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fix: vector subtraction bug #188

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Merged
physicshub merged 1 commit into from
Feb 17, 2026
Merged

fix: vector subtraction bug #188

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67 changes: 52 additions & 15 deletions simulations/VectorsOperations.jsx
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Original file line number Diff line number Diff line change
Expand Up @@ -249,7 +249,9 @@ export default function VectorsOperations() {

case "-": {
const Avec_sub = center.copy();
const Bvec_sub = p.constructor.Vector.sub(mouse, center);
const Bvec_sub = mouse.copy(); // B: origin -> mouse
const negAvec_sub = p.constructor.Vector.mult(Avec_sub, -1); // -A
const Rvec_sub = p.constructor.Vector.add(Bvec_sub, negAvec_sub); // R = B + (-A) = B - A

p.strokeWeight(strokeWeight);
p.stroke(strokeColor);
Expand All @@ -261,17 +263,40 @@ export default function VectorsOperations() {
p.strokeWeight(strokeWeight + 1);
p.line(center.x, center.y, mouse.x, mouse.y);
} else {
const Bneg = p.constructor.Vector.mult(Bvec_sub, -1);
const tip = p.constructor.Vector.add(Avec_sub, Bneg);
p.stroke(strokeColor);
p.strokeWeight(Math.max(1, strokeWeight - 0.5));
p.line(0, 0, Avec_sub.x, Avec_sub.y);
p.line(0, 0, Bneg.x, Bneg.y);

p.stroke(strokeColor);
p.strokeWeight(strokeWeight);
p.line(0, 0, Bvec_sub.x, Bvec_sub.y);

p.stroke(180, 180, 180, 180);
p.strokeWeight(strokeWeight);
p.drawingContext.setLineDash([6, 6]);
p.line(Avec_sub.x, Avec_sub.y, tip.x, tip.y);
p.line(Bneg.x, Bneg.y, tip.x, tip.y);
p.line(0, 0, negAvec_sub.x, negAvec_sub.y);

p.line(Bvec_sub.x, Bvec_sub.y, Rvec_sub.x, Rvec_sub.y);
p.line(negAvec_sub.x, negAvec_sub.y, Rvec_sub.x, Rvec_sub.y);
p.drawingContext.setLineDash([]);

p.noStroke();
p.fill(220);
p.textSize(14);
p.textAlign(p.CENTER, p.CENTER);
p.text("-A", negAvec_sub.x * 0.55, negAvec_sub.y * 0.55);

p.stroke(adjustColor(strokeColor));
p.strokeWeight(strokeWeight + 1);
p.line(0, 0, tip.x, tip.y);
p.line(0, 0, Rvec_sub.x, Rvec_sub.y);

p.stroke(adjustColor(strokeColor));
p.strokeWeight(Math.max(1, strokeWeight - 0.2));
p.line(Avec_sub.x, Avec_sub.y, Bvec_sub.x, Bvec_sub.y);

p.noStroke();
p.fill(255, 220, 120);
p.circle(Avec_sub.x, Avec_sub.y, 7);
}
break;
}
Expand Down Expand Up @@ -407,21 +432,33 @@ export default function VectorsOperations() {
}

case "-": {
const R =
visualizeMode === "triangle"
? p.constructor.Vector.sub(mouse, center)
: p.constructor.Vector.add(
A,
p.constructor.Vector.mult(B_from_center, -1)
);
const R = p.constructor.Vector.sub(mouse, center);
const Rpar = p.constructor.Vector.sub(B_from_origin, A);
const negA = p.constructor.Vector.mult(A, -1);
const Bcheck = p.constructor.Vector.add(A, R);
const checkErr = p.constructor.Vector.sub(
Bcheck,
B_from_origin
).mag();

info["Subtraction resultant R = B - A"] = `(${R.x.toFixed(
2
)}, ${R.y.toFixed(2)}) px`;
info["Parallelogram diagonal B + (-A)"] = `(${Rpar.x.toFixed(
2
)}, ${Rpar.y.toFixed(2)}) px`;
info["|R|"] = `${R.mag().toFixed(2)} px`;
info["Auxiliary -A"] = `(${negA.x.toFixed(2)}, ${negA.y.toFixed(
2
)}) px`;
info["Parallelogram check B = A + R"] = `(${Bcheck.x.toFixed(
2
)}, ${Bcheck.y.toFixed(2)}) px`;
info["Check error |(A + R) - B|"] = `${checkErr.toFixed(4)} px`;
info["Formula"] =
visualizeMode === "triangle"
? "Triangle: R = B - A (center→mouse)"
: "Parallelogram: R = A + (-B)";
: "Parallelogram: use B and -A as adjacent sides, diagonal is R = B + (-A)";
break;
}

Expand Down
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