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LU decomposition: Difference between revisions
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=={{header|Javascript}}==
{{works with|ES5 ES6}}
<lang javascript>
const mult=(a, b)=>{
let res = new Array(a.length);
for (let r = 0; r < a.length; ++r) {
res[r] = new Array(b[0].length);
for (let c = 0; c < b[0].length; ++c) {
res[r][c] = 0;
for (let i = 0; i < a[0].length; ++i)
res[r][c] += a[r][i] * b[i][c];
}
}
return res;
}
const lu = (mat) => {
let lower = [],upper = [],n=mat.length;;
for(let i=0;i<n;i++){
lower.push([]);
upper.push([]);
for(let j=0;j<n;j++){
lower[i].push(0);
upper[i].push(0);
}
}
for (let i = 0; i < n; i++) {
for (let k = i; k < n; k++){
let sum = 0;
for (let j = 0; j < i; j++)
sum += (lower[i][j] * upper[j][k]);
upper[i][k] = mat[i][k] - sum;
}
for (let k = i; k < n; k++) {
if (i == k)
lower[i][i] = 1;
else{
let sum = 0;
for (let j = 0; j < i; j++)
sum += (lower[k][j] * upper[j][i]);
lower[k][i] = (mat[k][i] - sum) / upper[i][i];
}
}
}
return [lower,upper];
}
const pivot = (m) =>{
let n = m.length;
let id = [];
for(let i=0;i<n;i++){
id.push([]);
for(let j=0;j<n;j++){
if(i===j)
id[i].push(1);
else
id[i].push(0);
}
}
for (let i = 0; i < n; i++) {
let maxm = m[i][i];
let row = i;
for (let j = i; j < n; j++)
if (m[j][i] > maxm) {
maxm = m[j][i];
row = j;
}
if (i != row) {
let tmp = id[i];
id[i] = id[row];
id[row] = tmp;
}
}
return id;
}
const luDecomposition=(A)=>{
const P = pivot(A);
A = mult(P,A);
return [...lu(A),P];
}
}</lang>
=={{header|jq}}==
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